Leetcode 1. Two Sum

1. Two Sum

• Total Accepted: 259837
• Total Submissions: 1043139
• Difficulty: Easy

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].

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

思路：直接看代码。

代码：

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int,int> imap;
        vector<int> res;
        int i,n=nums.size();
        for(i=0;i<n;i++){
            int tobeFound=target-nums[i];
            if(imap.find(tobeFound)!=imap.end()){
                res.push_back(imap[tobeFound]);
                res.push_back(i);
                return res;
            }
            imap[nums[i]]=i;
        }
        return res;
    }
};