LeetCode86|只出现一次的数字II

示例 1:

输入: [2,2,3,2]
输出: 3
示例 2:

输入: [0,1,0,1,0,1,99]
输出: 99

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

public class SingleNumberTest4 {
    public static void main(String[] args) {
        int[] nums = {2, 2, 3, 2};
        int singleNumber = singleNumber(nums);
        System.out.println("singleNumber = " + singleNumber);
    }

    public static int singleNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
            return -1;
        }
        HashMap<Integer, Integer> hashMap = new HashMap<>();
        for (int num : nums
        ) {
            hashMap.put(num, hashMap.getOrDefault(num, 0) + 1);
        }
        return hashMap.entrySet().stream().filter(x -> x.getValue() == 1).findFirst().get().getKey();
    }
}