LeetCode59|重复N次的元素

示例 1：

输入：[1,2,3,3]
输出：3
示例 2：

输入：[2,1,2,5,3,2]
输出：2
示例 3：

输入：[5,1,5,2,5,3,5,4]
输出：5
 

提示：

4 <= A.length <= 10000
0 <= A[i] < 10000
A.length 为偶数

 

import java.util.HashMap;
import java.util.HashSet;

public class RepeatedNTimesTest {
    public static void main(String[] args) {
        int[] A = {1, 2, 3, 3};
        int repeatedNTimes = repeatedNTimes2(A);
        System.out.println("repeatedNTimes = " + repeatedNTimes);
    }

    public static int repeatedNTimes(int[] A) {
        if (A == null || A.length < 4) {
            return -1;
        }
        int length = A.length;
        HashMap<Integer, Integer> hashMap = new HashMap<>(length);
        for (int j : A) {
            if (hashMap.containsKey(j)) {
                hashMap.put(j, hashMap.get(j) + 1);
            } else {
                hashMap.put(j, 1);
            }
        }
        return hashMap.entrySet().stream().filter(x -> x.getValue() > 1).findFirst().get().getKey();
    }

    public static int repeatedNTimes2(int[] A) {
        if (A == null || A.length < 4) {
            return -1;
        }
        HashSet<Integer> hashSet = new HashSet<>();
        for (int j : A) {
            if (!hashSet.add(j)) {
                return j;
            }
        }
        return -1;
    }
}