LeetCode【1】Two Sum

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

注意加粗的exactly，有且仅有一个。因此不必考虑太多。想的太多反而成了累赘。直接double循环是不行的，绝对超时啊。不多说，上代码：

vector<int> twoSum(vector<int> &numbers, int target)
{
    vector<int> index;
    map<int, int> m;
    for(int i = 0; i < numbers.size(); ++ i)
    {
        if(m.find(target - numbers[i]) != m.end())
        {
            index.push_back(m[target - numbers[i]] + 1);
            index.push_back(i + 1);
            break;
        }
        m[numbers[i]] = i;
    }
    return index;
}