[LeetCode]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

 

解法1：利用map

// TwoSum2.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <map>
using namespace std;
class Solution {
public:
	vector<int> twoSum(vector<int> &numbers, int target) {
		map<int, int>numMap;
		vector<int>res;
		map<int, int>::iterator map_lt;
		for (int i = 0; i < numbers.size(); i++)
		{
			numMap[numbers[i]] = i;
		}
		for (int i = 0; i < numbers.size(); i++)
		{
			map_lt = numMap.find(target - numbers[i]);
			if (map_lt != numMap.end() && numMap[target - numbers[i]] != i)
			{
				res.push_back(i+1);
				res.push_back(numMap[target - numbers[i]]+1);
				break;
			}
		}
		return res;
	}

};

int _tmain(int argc, _TCHAR* argv[])
{
	vector<int>nums;
	nums.push_back(2);
	nums.push_back(7);
	nums.push_back(11);
	nums.push_back(15);
	Solution ss;
	vector<int>res = ss.twoSum(nums,9);
	cout << res[0] << " " << res[1] << endl;
	system("pause");
	return 0;
}

　　解法2：先排序，然后前后2个指针

// TwoSum.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <vector>
#include<iostream>
#include <algorithm>
using namespace std;
class Node{
public:
	int num;
	int pos;
};
bool cmp(Node a, Node b)
{
	return a.num < b.num;
}
class Solution {
public:
	vector<int> twoSum(vector<int> &numbers, int target) {
		vector<Node>arrays;
		vector<int>res;
		for (int i = 0; i < numbers.size(); i++)
		{
			Node tempNode;
			tempNode.num = numbers[i];
			tempNode.pos = i;
			arrays.push_back(tempNode);
		}
		sort(arrays.begin(),arrays.end(),cmp);
		int i, j;
		for (i = 0, j = arrays.size() - 1; i != j;)
		{
			if (arrays[i].num + arrays[j].num == target)
			{
				int min, max;
				max = arrays[i].pos >= arrays[j].pos ? arrays[i].pos : arrays[j].pos;
				min = arrays[i].pos <= arrays[j].pos ? arrays[i].pos : arrays[j].pos;
				res.push_back(min+1);
				res.push_back(max+1);
				break;
			}
			else if (arrays[i].num + arrays[j].num > target)
			{
				j--;
			}
			else if (arrays[i].num + arrays[j].num < target)
			{
				i++;
			}
		}
		return res;
	}
	
};
int _tmain(int argc, _TCHAR* argv[])
{	
	Solution ss;
	vector<int>nums;
	nums.push_back(2);
	nums.push_back(7);
	nums.push_back(11);
	nums.push_back(15);
	vector<int>res = ss.twoSum(nums, 9);
	cout << "index1=" << res[0] << ", index2=" << res[1] << endl;
	system("pause");
	
}