CodeForces 14C Four Segments

题目链接：http://codeforces.com/problemset/problem/14/C

题意：给出四条线段的端点，若这四条线段能组成一个平行于坐标轴的矩形，且面积为正，输出YES，反之NO。

分析：讨论，一共四个点，两条平行x，两条平行y，每条线段长度必须重复不小于2次。

代码：

#include<cstdio>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdlib>
#include<iomanip>
#include<string>
#include<vector>
#include<map>
#include<string>
#include<iostream>
#include<algorithm>
using namespace std;
#define INF 0x3f3f3f3f
typedef long long ll;
#define Max(a,b) (a>b)?a:b
#define lowbit(x) x&(-x)

int main()
{
    map<int,map<int,int> >mp;
    map<int,int>mp1;
    int x[4],y[4],len=0,flag=1,x1[4],y1[4],xx=0,yy=0;
    for(int i=0; i<4; i++)
    {
        scanf("%d%d",&x[i],&y[i]);
        scanf("%d%d",&x1[i],&y1[i]);
        mp[x[i]][y[i]]++;
        mp[x1[i]][y1[i]]++;
        if((x1[i]==x[i])&&(y1[i]!=y[i]))
            yy++;
        else if((x1[i]!=x[i])&&(y1[i]==y[i]))
            xx++;
        else
            flag=0;
        len=abs(x1[i]-x[i]+y1[i]-y[i]);
        mp1[len]++;
    }
    if(xx!=yy)
        flag=0;
    for(int i=0; i<4; i++)
    {
        if(mp[x[i]][y[i]]!=2||mp[x1[i]][y1[i]]!=2)
            flag=0;
        len=abs(x1[i]-x[i]+y1[i]-y[i]);
        if(mp1[len]<2)
            flag=0;
    }
    if(flag)
        puts("YES");
    else
        puts("NO");
}