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package class_2022_05_1_week;
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import java.util.Arrays;
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import java.util.HashSet;
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// 来自学员问题，真实大厂面试题
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// 1、2、3...n-1、n、n、n+1、n+2...
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// 在这个序列中，只有一个数字有重复(n)
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// 这个序列是无序的，找到重复数字n
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// 这个序列是有序的，找到重复数字n
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public class Code03_FindDuplicateOnlyOne {
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// 为了测试
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// 绝对正确，但是直接遍历+哈希表，没有得分的方法
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public static int right(int[] arr) {
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HashSet<Integer> set = new HashSet<>();
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for (int num : arr) {
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if (set.contains(num)) {
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return num;
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}
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set.add(num);
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}
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return -1;
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}
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// 符合题目要求的、无序数组，找重复数
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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 findDuplicate(int[] arr) {
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if (arr == null || arr.length < 2) {
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return -1;
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}
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int slow = arr[0];
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int fast = arr[arr[0]];
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while (slow != fast) {
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slow = arr[slow];
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fast = arr[arr[fast]];
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}
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// slow == fast
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fast = 0;
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while (slow != fast) {
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fast = arr[fast];
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slow = arr[slow];
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}
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// 再相遇！一个结论
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return slow;
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}
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// 符合题目要求的、有序数组，找重复数
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// 时间复杂度O(logN)，额外空间复杂度O(1)
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public static int findDuplicateSorted(int[] arr) {
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if (arr == null || arr.length < 2) {
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return -1;
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}
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int l = 0;
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int r = arr.length - 1;
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int m = 0;
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int ans = -1;
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while (l <= r) {
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m = (l + r) / 2;
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if ((m - 1 >= 0 && arr[m - 1] == arr[m]) || (m + 1 < arr.length && arr[m + 1] == arr[m])) {
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ans = arr[m];
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break;
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}
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if (m - l == arr[m] - arr[l]) {
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l = m + 1;
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} else {
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r = m - 1;
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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 n) {
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int[] ans = new int[n + 1];
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for (int i = 0; i < n; i++) {
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ans[i] = i + 1;
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}
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ans[n] = (int) (Math.random() * n) + 1;
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for (int i = n; i > 0; i--) {
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int j = (int) (Math.random() * (i + 1));
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int tmp = ans[i];
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ans[i] = ans[j];
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ans[j] = tmp;
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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 void main(String[] args) {
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int N = 10;
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int testTime = 5000;
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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[] arr = randomArray((int) (Math.random() * N) + 1);
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if (right(arr) != findDuplicate(arr)) {
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System.out.println("未排序情况出错!");
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}
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Arrays.sort(arr);
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if (right(arr) != findDuplicateSorted(arr)) {
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System.out.println("排序情况出错!");
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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(right(arr));
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System.out.println(findDuplicateSorted(arr));
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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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