leetcode 136. Single Number

题意

给定一个非空整数数组，除了某个元素只出现一次以外，其余每个元素均出现两次。找出那个只出现了一次的元素。

Example 1:

Input: nums = [2,2,1]
Output: 1

Example 2:

Input: nums = [4,1,2,1,2]
Output: 4

Example 3:

Input: nums = [1]
Output: 1

解

a ^ b ^ b = a

根据异或运算的性质可知，把所有元素参与异或运算，即得到答案。

// Runtime: 1 ms, faster than 74.06% of Java online submissions for Single Number.
//Memory Usage: 39.3 MB, less than 6.29% of Java online submissions for Single Number.
public int singleNumber(int[] nums) { 
    if (nums == null || nums.length == 0)
        return 0;
    int rst = nums[0];
    for (int i = 1; i < nums.length; i++)
        rst ^= nums[i];
    return rst;
}

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