136. Single Number

找到一个数组中只出现一次的元素，使用异或实现。
Runtime: 80 ms, faster than 79.41%
Memory Usage: 40.3 MB, less than 5.04%

/**
 * @param {number[]} nums
 * @return {number}
 */
var singleNumber = function(nums) {
    return nums.reduce((a, b) => a ^ b)
};

/**
 * @param {number[]} nums
 * @return {number}
 */
var singleNumber = function(nums) {
    let res = 0
    let len = nums.length
    for (let i = 0; i < len; i++) {
        res ^= nums[i]
    }
    return res
};