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package class07;
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import java.util.Arrays;
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import java.util.HashSet;
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public class Code04_Power2Diffs {
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/*
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* 给定一个有序数组arr，其中值可能为正、负、0。 返回arr中每个数都平方之后不同的结果有多少种？
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*
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* 给定一个数组arr，先递减然后递增，返回arr中有多少个绝对值不同的数字？
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*
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*/
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// 时间复杂度O(N)，额外空间复杂度O(N)
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public static int diff1(int[] arr) {
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if (arr == null || arr.length == 0) {
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return 0;
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}
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HashSet<Integer> set = new HashSet<>();
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for (int cur : arr) {
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set.add(cur * cur);
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}
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return set.size();
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}
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// 时间复杂度O(N)，额外空间复杂度O(1)
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public static int diff2(int[] arr) {
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int N = arr.length;
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int L = 0;
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int R = N - 1;
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int count = 0;
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int leftAbs = 0;
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int rightAbs = 0;
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while (L <= R) {
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count++;
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leftAbs = Math.abs(arr[L]);
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rightAbs = Math.abs(arr[R]);
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if (leftAbs < rightAbs) {
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while (R >= 0 && Math.abs(arr[R]) == rightAbs) {
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R--;
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}
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} else if (leftAbs > rightAbs) {
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while (L < N && Math.abs(arr[L]) == leftAbs) {
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L++;
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}
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} else {
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while (L < N && Math.abs(arr[L]) == leftAbs) {
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L++;
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}
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while (R >= 0 && Math.abs(arr[R]) == rightAbs) {
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R--;
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}
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}
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}
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return count;
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}
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// for test
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public static int[] randomSortedArray(int len, int value) {
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int[] ans = new int[(int) (Math.random() * len) + 1];
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for (int i = 0; i < ans.length; i++) {
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ans[i] = (int) (Math.random() * value) - (int) (Math.random() * value);
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}
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Arrays.sort(ans);
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return ans;
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}
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// for test
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public static void printArray(int[] arr) {
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for (int cur : arr) {
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System.out.print(cur + " ");
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}
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System.out.println();
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}
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public static void main(String[] args) {
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int len = 100;
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int value = 500;
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int testTimes = 200000;
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System.out.println("test begin");
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for (int i = 0; i < testTimes; i++) {
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int[] arr = randomSortedArray(len, value);
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int ans1 = diff1(arr);
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int ans2 = diff2(arr);
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if (ans1 != ans2) {
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printArray(arr);
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System.out.println(ans1);
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System.out.println(ans2);
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System.out.println("Oops!");
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break;
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}
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}
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System.out.println("test finish");
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}
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}
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