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.

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

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

//way #1
//O(n2) 
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        for (auto i = 0; i != nums.size() -1 ; ++i)
        {
            for (auto j = i+1; j != nums.size(); ++j)
            {
                if (target == (nums[i] + nums[j]))
                {
                    result.push_back(i);
                    result.push_back(j);
                }
            }
        }
        return result;
    }
};

//way #2
//O(n)
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        map<int,int> imap;
        for (int i = 0; i != nums.size(); ++i)
        {
            imap.insert(make_pair(nums[i], i));
        }
        for (int i = 0;i != nums.size(); ++i)
        {
            int complement = target - nums[i];
            auto it = imap.find(complement);
            if (it != imap.end() && it->second != i)
            {
                result.push_back(i);
                result.push_back(it->second);
                break;
            }
        }
        return result;
    }
};