1. Two Sum

python
主要是字典的用法

class Solution:
      def twoSum(self, nums, target):
          d = {}
          for i, num in enumerate(nums):
              if target - num in d:
                  return [d[target-num], i]
              d[num] = i
        

c++
主要是unordered_map的用法

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> m;
        vector<int> v;
        for(int i = 0; i < nums.size(); ++i){
            int temp = target - nums[i];
            auto it = m.find(temp);
            if(it != m.end()){
                v.push_back(it->second);
                v.push_back(i);
                return v;
            }
            m[nums[i]] = i;
        }

        return v;
    }
};