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package class05;
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// 这道题直接在leetcode测评：
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// https://leetcode.com/problems/count-of-range-sum/
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public class Code01_CountOfRangeSum {
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public static int countRangeSum(int[] nums, int lower, int upper) {
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if (nums == null || nums.length == 0) {
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return 0;
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}
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long[] sum = new long[nums.length];
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sum[0] = nums[0];
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for (int i = 1; i < nums.length; i++) {
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sum[i] = sum[i - 1] + nums[i];
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}
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return process(sum, 0, sum.length - 1, lower, upper);
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}
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public static int process(long[] sum, int L, int R, int lower, int upper) {
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if (L == R) {
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return sum[L] >= lower && sum[L] <= upper ? 1 : 0;
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}
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int M = L + ((R - L) >> 1);
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return process(sum, L, M, lower, upper) + process(sum, M + 1, R, lower, upper)
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+ merge(sum, L, M, R, lower, upper);
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}
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public static int merge(long[] arr, int L, int M, int R, int lower, int upper) {
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int ans = 0;
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int windowL = L;
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int windowR = L;
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// [windowL, windowR)
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for (int i = M + 1; i <= R; i++) {
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long min = arr[i] - upper;
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long max = arr[i] - lower;
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while (windowR <= M && arr[windowR] <= max) {
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windowR++;
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}
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while (windowL <= M && arr[windowL] < min) {
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windowL++;
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}
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ans += windowR - windowL;
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}
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long[] help = new long[R - L + 1];
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int i = 0;
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int p1 = L;
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int p2 = M + 1;
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while (p1 <= M && p2 <= R) {
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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 ans;
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}
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}
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