[leetcode] 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].

解法一：

思想就是建立hash table，每次都hash table找差值。

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

}
};