leetcode-136 只出现一次的数字 Java

https://leetcode-cn.com/problems/single-number/solution/xue-suan-fa-jie-guo-xiang-dui-yu-guo-cheng-bu-na-y/

方法一：哈希表

class Solution {
    public int singleNumber(int[] nums) {
        Map<Integer, Integer> map = new HashMap<>();
        for (Integer i : nums) {
            Integer count = map.get(i);
            count = count == null ? 1: ++count;
            map.put(i, count);
        }
        for (Integer i: map.keySet()) {
            Integer count = map.get(i);
            if (count == 1) {
                return i;
            }
        }
        return -1;
    }
}

方法二：亦或

class Solution {
    public int singleNumber(int[] nums) {
        int ans = nums[0];
        if (nums.length > 1) {
            for (int i = 1; i < nums.length; i++) {
                ans ^= nums[i];
            }
        }
        return ans;
    }
}