1 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].

本题的知识点： 可以用hash table来进行快速查找，从而降低时间复杂度

最终提交的代码：

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        
        vector<int> indices;
            
        //with hash map
        map<int,int> mydict;
        
        for(int i=0;i<nums.size();i++)
        {
            mydict[nums[i]] = i;
        }
        
        for(int i=0;i<nums.size();i++)
        {
            int res = target - nums[i];
            auto it = mydict.find(res);
            if(it != mydict.end() && it->second != i)
            {
                indices.push_back(i);
                indices.push_back(it->second);
                return indices;
            }
        }
        
        return indices;
        
    }
};