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package class_2022_03_2_week;
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// 来自微软
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// 给定一个数组arr，给定一个正数M
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// 如果arr[i] + arr[j]可以被M整除，并且i < j，那么(i,j)叫做一个M整除对
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// 返回arr中M整除对的总数量
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public class Code05_NumberOfDivisibleByM {
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public static int num1(int[] arr, int m) {
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int n = arr.length;
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int ans = 0;
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for (int i = 0; i < n; i++) {
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for (int j = i + 1; j < n; j++) {
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if (Math.abs(arr[i] + arr[j]) % m == 0) {
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ans++;
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}
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}
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}
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return ans;
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}
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public static int num2(int[] arr, int m) {
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int n = arr.length;
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int[] cnts = new int[m];
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int ans = 0;
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for (int i = n - 1; i >= 0; i--) {
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int cur = (arr[i] % m + m) % m;
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ans += cnts[(m - cur) % m];
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cnts[cur]++;
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}
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return ans;
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}
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// 为了测试
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public static int[] randomArray(int n, int v) {
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int[] arr = new int[n];
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for (int i = 0; i < n; i++) {
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arr[i] = (int) (Math.random() * v) - (int) (Math.random() * v);
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}
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return arr;
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}
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public static void main(String[] args) {
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int len = 50;
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int value = 50;
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int testTime = 20000;
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System.out.println("测试开始");
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for (int i = 0; i < testTime; i++) {
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int n = (int) (Math.random() * len) + 1;
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int[] arr = randomArray(n, value);
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int m = (int) (Math.random() * value) + 1;
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int ans1 = num1(arr, m);
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int ans2 = num2(arr, m);
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if (ans1 != ans2) {
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System.out.println("出错了!");
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for (int num : arr) {
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System.out.print(num + " ");
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}
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System.out.println();
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System.out.println("m = " + m);
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System.out.println(ans1);
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System.out.println(ans2);
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break;
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}
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}
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System.out.println("测试结束");
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}
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}
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