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

直接暴力法O（n*n）超時，所以需採用hashmap，這裏採用map來存儲數據並進行搜索，其實現爲

 1 class Solution {
 2 public:
 3     vector<int> twoSum(vector<int>& nums, int target) {
 4        vector<int> res;
 5        map<int,int> tmp;
 6        for(int i=0;i<nums.size();i++)
 7        {
 8            if(!tmp.count(nums[i]))
 9                tmp.insert(pair<int,int>(nums[i],i+1));
10            if(tmp.count(target-nums[i]))
11            {
12                int n=tmp[target-nums[i]];
13                if(n<i+1)
14                {
15                    res.push_back(n);
16                    res.push_back(i+1);
17                    return res;
18                }
19            }
20        }
21        return res;
22     }
23 };

 

紅黑樹。