LeetCode #151 Two Sum

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原文链接：http://www.cnblogs.com/Haeckel/p/3893392.html

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#数据结构与算法

本文详细解析了LeetCode上的经典题目TwoSum，提供了高效的算法思路和C++代码实现，通过排序和双指针技巧找到数组中两个数相加等于目标值的下标。

# LeetCode #151 Two Sum

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：

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        vector<int> temp = numbers;
        sort(temp.begin(), temp.end());
        //cout<<*numbers.begin()<<numbers.at(3)<<endl;
        int index1,index2;
        int i = 0,j = temp.size()-1;
        while(i < j){
        //cout<<i<<j<<endl;
        int sum = temp[i] + temp[j];
        if(sum == target){
            break;
        }else if(sum > target){
            j--;
        }else{
            i++;
        }
    

        for(int k = 0; k < temp.size(); k++){
            if(numbers[k] == temp[i])
                {index1 = k+1;break;}
        }
        for(int k = temp.size()-1; k >= 0; k--){
            //cout<<k<<endl;
            if(numbers[k] == temp[j])
                {index2 = k+1;break;}
        }
        if(index1 > index2){
            int temp = index1;
            index1 = index2;
            index2 = temp;
        }
        vector<int> result;
        result.push_back(index1);
        result.push_back(index2);
        return result;
    }
};

int main()
{
    //cout << "Hello world!" << endl;
    int nums[4] = {4,3,2,1};
    vector<int> numbers(&nums[0], &nums[4]);
    Solution solution;
    vector<int> re = solution.twoSum(numbers, 5);
    cout<<re.at(0)<<" "<<re.at(1);
    return 0;
}