1. Two Sum

题目来源【Leetcode】

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].

这道题我是用数组来存储pair，first为nums[i]的数，second为该数在nums中原来的下标，然后对数组进行排序，再来进行查找。

class Solution {public:    vector<int> twoSum(vector<int>& nums, int target) {        vector<pair<int,int>>n;        for(int i = 0;  i < nums.size(); i++){            pair<int,int>p;            p.first = nums[i];            p.second = i;            n.push_back(p);        }        sort(n.begin(),n.end());        int l,h;        l = 0;        h = nums.size()-1;        while(target != n[l].first+n[h].first && l <= h){            if(target < n[l].first+n[h].first) h--;            if(target > n[l].first+n[h].first) l++;        }        vector<int>re;        re.push_back(n[l].second);        re.push_back(n[h].second);        return re;    }};