Swift 只出现一次的数字 - LeetCode

1^1 = 0
1^1^2 = 2
1^1^2^2^3 = 3
0和任何数异或得其本身

class Solution {
    func singleNumber(_ nums: [Int]) -> Int {
        var single = 0
        nums.forEach { (num) in
           single = single ^ num
        }
        return single
    }
}