題目連結: https://leetcode.com/problems/single-number/

XOR方法:

    func singleNumber(_ nums: [Int]) -> Int {
		return nums.reduce(0) {
			$0 ^ $1
		}	
    }

使用Dictionary方法:

    func singleNumber(_ nums: [Int]) -> Int {
        if nums.count == 0 { return -1 }
        else if nums.count == 1 { return nums[0] }
        else {
        	var dic: [Int: Int] = [:]
        	for item in nums {
        		dic[item, default: 0] = dic[item, default: 0] + 1
        	}
        	for (key, val) in dic {
        		if val == 1 {
        			return key
        		}
        	}
        	return -1
        }
    }


參考:
https://leetcode.com/problems/single-number/discuss/314884/My-4-Swift-Solutions