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416 lines
10 KiB
416 lines
10 KiB
package leo.class03_04;
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import leo.util.ArrayUtil;
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/**
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* @author Leo
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* @ClassName SmallSum
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* @DATE 2020/11/23 10:46 上午
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* @Description 小和问题
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* 在一个数组中，每一个数左边比当前数小的数累加起来，叫做这个数组的小和。求一个数组的小和
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*/
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class SmallSum {
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public static int smallSum(int[] arr) {
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if (arr.length == 0 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int L, int R) {
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if (L == R) {
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return 0;
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}
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int mid = L + ((R - L) >> 1);
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return process(arr, L, mid)
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+ process(arr, mid + 1, R)
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+ merge(arr, L, mid, R);
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}
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/**
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* 左<右,小和=(右总长-有下标+1)*左;
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* 左<右 左进入help数组,左移动下标,
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* 左等于右或左大于右,右进help数组,右移动下标.
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*/
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private static int merge(int[] arr, int l, int m, int r) {
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int[] help = new int[r - l + 1];
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int p1 = l;
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int p2 = m + 1;
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int res = 0;
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int i = 0;
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while (p1 <= m && p2 <= r) {
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res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return res;
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}
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}
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class SmallSum1{
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int l, int r) {
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if (l == r) {
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return 0;
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}
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int mid = l + ((r - l) >> 1);
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return process(arr, l, mid)
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+ process(arr, mid + 1, r)
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+ merge(arr, l, mid, r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int p1 = l;
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int p2 = m+1;
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int i = 0;
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int[] help = new int[r - l + 1];
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int res = 0;
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while (p1 <= m && p2 <= r) {
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res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return res;
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}
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}
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class SmallSum2 {
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int l, int r) {
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if (l == r) {
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return 0;
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}
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int mid = l + ((r - l) >> 1);
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return process(arr, l, mid) +
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process(arr, mid + 1, r) +
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merge(arr, l, mid, r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int res = 0;
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int p1 = l;
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int p2 = m + 1;
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int i = 0;
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int[] help = new int[r - l + 1];
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while (p1 <= m && p2 <= r) {
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res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while(p1<=m){
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help[i++] = arr[p1++];
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}
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while(p2<=r){
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return res;
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}
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}
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class SmallSum3{
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int l, int r) {
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if (l == r) {
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return 0;
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}
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int mid = l + ((r - l) >> 1);
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return process(arr, l, mid) + process(arr, mid + 1, r) + merge(arr, l, mid, r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int i = 0;
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int[] help = new int[r - l + 1];
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int p1 = l;
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int p2 = m + 1;
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int sum = 0;
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while (p1 <= m && p2 <= r) {
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sum += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return sum;
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}
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}
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class SmallSum4{
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int l, int r) {
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if (l == r) {
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return 0;
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}
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int m = l + ((r - l) >> 1);
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return process(arr, l, m) + process(arr, m + 1, r)+merge(arr,l,m,r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int sum = 0;
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int[] help = new int[r - l + 1];
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int p1 = l;
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int p2 = m + 1;
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int i = 0;
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while (p1 <= m && p2 <= r) {
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sum += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return sum;
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}
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}
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class SmallSum5{
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int l, int r) {
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if (l == r) {
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return 0;
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}
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int m = l + ((r - l) >> 1);
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return process(arr, l, m) + process(arr, m + 1, r) + merge(arr, l, m, r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int res = 0;
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int p1 = l;
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int p2 = m + 1;
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int i = 0;
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int[] help = new int[r - l + 1];
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while (p1 <= m && p2 <= r) {
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res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return res;
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}
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}
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class SmallSum6{
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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private static int process(int[] arr, int l, int r) {
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if (l == r) {
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return 0;
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}
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int m = l + ((r - l) >> 1);
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return process(arr, l, m) + process(arr, m + 1, r) + merge(arr, l, m, r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int[] help = new int[r - l + 1];
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int res = 0;
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int p1 = l;
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int p2 = m + 1;
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int i = 0;
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while (p1 <= m && p2 <= r) {
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res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return res;
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}
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}
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class SmallSum7 {
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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return process(arr, 0, arr.length - 1);
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}
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public static int process(int[] arr, int l, int r) {
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if (l >= r) {
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return 0;
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}
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int m = l + ((r - l) >> 1);
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return process(arr, l, m) + process(arr, m + 1, r) + merge(arr, l, m, r);
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}
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private static int merge(int[] arr, int l, int m, int r) {
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int res = 0;
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int p1 = l;
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int p2 = m + 1;
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int i = 0;
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int[] help = new int[r - l + 1];
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while (p1 <= m && p2 <= r) {
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res += arr[p1] < arr[p2] ? (r - p2 + 1) * arr[p1] : 0;
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help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
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}
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while (p1 <= m) {
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help[i++] = arr[p1++];
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}
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while (p2 <= r) {
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help[i++] = arr[p2++];
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}
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for (i = 0; i < help.length; i++) {
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arr[l + i] = help[i];
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}
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return res;
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}
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}
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class TestSmallSum{
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public static int smallSum(int[] arr) {
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if (arr.length < 2 || arr == null) {
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return 0;
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}
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int res = 0;
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for (int i = 1; i < arr.length; i++) {
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for (int j = 0; j < i; j++) {
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res += arr[j] < arr[i] ? arr[j] : 0;
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}
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}
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for (int i = 0; i < arr.length-1; i++) {
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for (int j = i + 1; j < arr.length; j++) {
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if (arr[i] > arr[j]) {
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swap(arr, i, j);
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}
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}
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}
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return res;
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}
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public static void swap(int[] arr, int i, int j) {
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if (i == j||arr[i]==arr[j]) {
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return;
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}
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arr[i] = arr[i] ^ arr[j];
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arr[j] = arr[i] ^ arr[j];
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arr[i] = arr[i] ^ arr[j];
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}
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}
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class TestMain {
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public static void main(String[] args){
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int testTime = 1000;
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int range = 50;
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int maxSize = 100;
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System.out.println("start!");
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for (int i = 0; i < testTime; i++) {
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int[] arr = ArrayUtil.randomArray(maxSize, range);
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int[] copyArray = ArrayUtil.copyArray(arr);
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int sum = SmallSum7.smallSum(arr);
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int testSum = TestSmallSum.smallSum(copyArray);
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if (testSum != sum) {
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System.out.println("sum :" + sum + ", testSum : " + testSum);
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break;
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}
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if (!ArrayUtil.isEqual(arr, copyArray)) {
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System.out.println("arr :" + arr );
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System.out.println("copyArray : " + copyArray);
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break;
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}
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}
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System.out.println("end!");
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}
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}
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