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package class41;
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// 来自小红书
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// 一个无序数组长度为n，所有数字都不一样，并且值都在[0...n-1]范围上
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// 返回让这个无序数组变成有序数组的最小交换次数
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public class Code01_MinSwapTimes {
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// 纯暴力，arr长度大一点都会超时
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// 但是绝对正确
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public static int minSwap1(int[] arr) {
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return process1(arr, 0);
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}
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// 让arr变有序，最少的交换次数是多少！返回
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// times, 之前已经做了多少次交换
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public static int process1(int[] arr, int times) {
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boolean sorted = true;
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for (int i = 1; i < arr.length; i++) {
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if (arr[i - 1] > arr[i]) {
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sorted = false;
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break;
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}
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}
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if (sorted) {
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return times;
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}
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// 数组现在是无序的状态！
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if (times >= arr.length - 1) {
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return Integer.MAX_VALUE;
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}
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int ans = Integer.MAX_VALUE;
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for (int i = 0; i < arr.length; i++) {
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for (int j = i + 1; j < arr.length; j++) {
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swap(arr, i, j);
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ans = Math.min(ans, process1(arr, times + 1));
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swap(arr, i, j);
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}
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}
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return ans;
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}
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public static void swap(int[] arr, int i, int j) {
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int tmp = arr[i];
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arr[i] = arr[j];
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arr[j] = tmp;
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}
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// 已知arr中，只有0~n-1这些值，并且都出现1次
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public static int minSwap2(int[] arr) {
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int ans = 0;
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for (int i = 0; i < arr.length; i++) {
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while (i != arr[i]) {
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swap(arr, i, arr[i]);
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ans++;
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}
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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 len) {
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int[] arr = new int[len];
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for (int i = 0; i < len; i++) {
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arr[i] = i;
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}
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for (int i = 0; i < len; i++) {
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swap(arr, i, (int) (Math.random() * len));
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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 n = 6;
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int testTime = 2000;
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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 len = (int) (Math.random() * n) + 1;
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int[] arr = randomArray(len);
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int ans1 = minSwap1(arr);
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int ans2 = minSwap2(arr);
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if (ans1 != ans2) {
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System.out.println("出错了!");
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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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