【Leetcode】Two Sum

题目：

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

代码1（复杂度O(n^2)，超时）：

class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        vector<int> index;
        for(int i=0;i<numbers.size();i++){
            vector<int>::iterator itr=find(numbers.begin()+i+1,numbers.end(),target-numbers[i]);
            if(itr!=numbers.end()&&(itr-numbers.begin())>i){
                index.push_back(i+1);
                index.push_back(itr-numbers.begin()+1);
                return index;
            }
        }
        return index;
    }
};

class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        vector<int> result;
        map<int,int> index;
        for(int i=0;i<numbers.size();i++){
            index[numbers[i]]=i;
        }
        for(int i=0;i<numbers.size();i++){
            map<int,int>::iterator itr=index.find(target-numbers[i]);
            if(itr!=index.end()&&index[target-numbers[i]]!=i){
                result.push_back(i+1);
                result.push_back(index[target-numbers[i]]+1);
                return result;
            }
        }
        return result;
    }
};

【Leetcode】Two Sum,布布扣,bubuko.com

【Leetcode】Two Sum

原文：http://blog.csdn.net/ussam/article/details/22323989