LeetCode-E-Two Sum

题意

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, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

解法

排序 ＋ 双指针

实现

bool mycompare(pair<int,int> a, pair<int,int> b){    return a.first < b.first;}class Solution {public:    vector<int> twoSum(vector<int>& nums, int target) {        vector<int> result;        if(nums.size() == 0) return result;        vector<pair<int,int>> ivector;        for(int i = 0; i < nums.size(); ++i){            ivector.push_back(make_pair(nums[i],i));        }        std::sort(ivector.begin(),ivector.end(),mycompare);        int start = 0;         int end = ivector.size() - 1;        while(start < end){            int sum = ivector[start].first + ivector[end].first;            if(sum == target){                result.push_back(ivector[start].second);                result.push_back(ivector[end].second);                return result;            }else if(sum < target){                ++start;            }else --end;        }        return result;    }};