Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

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

注意：emplace函数可以直接打包插入unordered_map。