leetcode136

public class Solution {
    public int SingleNumber(int[] nums) {
        Dictionary<int, int> dic = new Dictionary<int, int>();
            foreach (var n in nums)
            {
                if (!dic.ContainsKey(n))
                {
                    dic.Add(n, 1);
                }
                else
                {
                    dic[n]++;
                }
            }

            var result = 0;

            foreach (var d in dic)
            {
                if (d.Value == 1)
                {
                    result = d.Key;
                }
            }
            //Console.WriteLine(result);
            return result;
    }
}

https://leetcode.com/problems/single-number/#/description

C++代码：

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        set<int> SET;
        for (auto n : nums)
        {
            if (SET.find(n) == SET.end())
            {
                SET.insert(n);
            }
            else
            {
                SET.erase(n);
            }
        }
        for (auto s : SET)
        {
            return    s;
        }
    }
};

补充一个python的实现：

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        a = 0
        for i in nums:
            a ^= i
        return a

原理：x ^ 0 = x，x ^ x = 0