# 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].


Solution:

Use a map to save all positions of nums, try to find target-nums[i].

class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
map<int,int> pos;

for(int i=0;i<nums.size();i++){

if(pos.find(target-nums[i]) != pos.end()){
return vector<int>{pos[target-nums[i]], i};
}

pos[nums[i]] = i;
}

return vector<int>();
}
};