LeetCode 3Sum

想法：先排序，先考虑0的情况（三个以上连续的0），再考虑绝对值相同的数值，再考虑不包括0的情况，两个正数和为一个负数，或者两个负数的和为一个正数。这样的结果会包含重复的元素，最后再去掉重复的。提交时自己写的针对容器的容器去重和排序在本地VS2008下编译通过，但是提交不通过，去掉自己的比较函数，直接去重居然也好使，通过了。

// LeetCode_3Sum.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

bool lessthan(const vector<int> &vec1,const vector<int> &vec2)
{
	return vec1[0]<vec2[0];
}
bool equal(const vector<int> &vec1,const vector<int> &vec2)
{
	int lenvec1 = vec1.size();
	int lenvec2 = vec2.size();
	if (lenvec1 != lenvec2)
		return false;
	for (int i=0;i<lenvec2;i++)
	{
		if (vec1[i] != vec2[i])
		{
			return false;
		}
	}
	return true;
}

vector<vector<int> > threeSum(vector<int> &num) {
	int numlen = num.size();
	sort(num.begin(),num.end());//sort(num.begin(),num.end(),less<int>())
	bool flag;
	vector<vector<int>> ret;
	vector<int> retelem;
	vector<int>::iterator pos = find(num.begin(),num.end(),0);
	vector<int>::iterator conterpos;
	if (pos == num.end())
		flag = false;
	else
		flag = true;
	if (flag)
	{
		vector<int>::iterator iterzero = find(num.begin(),num.end(),0);
		if(iterzero+2<num.end()&&*(iterzero+2)==0)
		{
			retelem.push_back(0);
			retelem.push_back(0);
			retelem.push_back(0);
			ret.push_back(retelem);
			retelem.clear();
		}
		vector<int>::iterator iter = num.begin();
		while(iter!=pos)
		{
			conterpos = find(pos,num.end(),-*iter);
			if (conterpos!=num.end())
			{
				retelem.push_back(*iter);
				retelem.push_back(0);
				retelem.push_back(-*iter);
				ret.push_back(retelem);
				retelem.clear();
			}
			iter++;
		}
	}
	vector<int>::iterator iteredge = num.begin();
	while(iteredge!=num.end()&&*iteredge<0) iteredge++;
	if (iteredge==num.begin()||iteredge==num.end())
	{
		return ret;
	}
	vector<int>::iterator iter1front = num.begin();
	vector<int>::iterator iter2front = iteredge;
	vector<int>::iterator iter1back,iter2back;
	while (iter1front != iteredge)
	{
		iter1back = iteredge;
		iter2back = num.end()-1;
		while(iter1back<iter2back)
		{
			if (*iter1back + *iter2back == -*iter1front)
			{
				retelem.push_back(*iter1front);
				retelem.push_back(*iter1back);
				retelem.push_back(*iter2back);
				ret.push_back(retelem);
				retelem.clear();
				iter2back--;
				iter1back++;
			}
			else
			{
				if (*iter1back + *iter2back > -*iter1front)
					iter2back--;
				else
					iter1back++;
			}
		}
		iter1front++;
	}
	iter1back = iteredge;
	while(iter1back != num.end())
	{
		iter1front = num.begin();
		iter2front = iteredge-1;
		while(iter1front<iter2front)
		{
			if (*iter1front + *iter2front == -*iter1back)
			{
				retelem.push_back(*iter1front);
				retelem.push_back(*iter2front);
				retelem.push_back(*iter1back);
				ret.push_back(retelem);
				retelem.clear();
				iter1front++;
				iter2front--;
			}
			else
			{
				if (*iter1front + *iter2front > -*iter1back)
					iter2front--;
				else
					iter1front++;
			}
		}
		iter1back++;
	}
	sort(ret.begin(),ret.end());//sort(ret.begin(),ret.end(),lessthan);
	ret.erase(unique(ret.begin(),ret.end()),ret.end());//ret.erase(unique(ret.begin(),ret.end(),equal),ret.end());

	return ret;
}

int _tmain(int argc, _TCHAR* argv[])
{
	vector<int> vec;
	vec.push_back(-1);//{-1 0 1 2 -1 -4}
	vec.push_back(0);
	//vec.push_back(0);
	//vec.push_back(0);
	vec.push_back(0);
	vec.push_back(1);
	vec.push_back(2);
	vec.push_back(-1);
	vec.push_back(-4);
	vector<vector<int> > ret;
	ret = threeSum(vec);
	int retlen = ret.size();
	for (int i=0;i<retlen;i++)
	{
		for(int j=0;j<ret[i].size();j++)
			cout<<ret[i][j]<<" ";
		cout<<endl;
	}
	system("pause");
	return 0;
}