LeetCode: Two Sum 题解

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

解法：

1. 暴力BF，直接超时

2. hash，用映射 STL： map + vector

class Solution {

public:

    vector<int> twoSum(vector<int> &numbers, int target) {

          map<int ,int> match;

          vector<int> ans;

          ans.clear();

          int i;

          for(i=0;i<numbers.size();i++)

              match[numbers[i]] = i+1;  // 记录位置

          for(i=0;i<numbers.size();i++)

          {

if(match.find(target - numbers[i]) != match.end()  && i+1 != match[target - numbers[i]])  // map映射

               {

                   ans.push_back(i+1);

                   ans.push_back(match[target-numbers[i]]);

                   break;

               }

          }

          return ans;

    }

};

LeetCode: Two Sum 题解