题目地址：

https://www.lintcode.com/problem/largest-number-x-which-occurs-x-times/description

给定一个数组，求本身数值与其出现次数相等的那些数里最大的那个。用哈希表即可。代码如下：

import java.util.HashMap;
import java.util.Map;public class Solution {/*** @param arr: an array of integers* @return: return the biggest value X, which occurs in A exactly X times.*/public int findX(int[] arr) {// write your code hereif (arr == null || arr.length == 0) {return 0;}Map<Integer, Integer> map = new HashMap<>();for (int x : arr) {map.put(x, map.getOrDefault(x, 0) + 1);}int res = 0;for (Map.Entry<Integer, Integer> entry : map.entrySet()) {int k = entry.getKey(), v = entry.getValue();if (k == v) {res = Math.max(res, k);}}return res;}
}

时空复杂度O(n)O(n)O(n)。

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【Lintcode】1880. Largest Number X Which Occurs X Times

题目地址：

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