(简单) POJ 2492 A Bug's Life，二分染色。

Description

Background 
Professor Hopper is researching the sexual behavior of a rare species of bugs. He assumes that they feature two different genders and that they only interact with bugs of the opposite gender. In his experiment, individual bugs and their interactions were easy to identify, because numbers were printed on their backs. 
Problem 
Given a list of bug interactions, decide whether the experiment supports his assumption of two genders with no homosexual bugs or if it contains some bug interactions that falsify it.

　　判断奇环，二分染色bfs，并查集都可做。

代码如下：

// ━━━━━━神兽出没━━━━━━
//      ┏┓       ┏┓
//     ┏┛┻━━━━━━━┛┻┓
//     ┃           ┃
//     ┃     ━     ┃
//     ████━████   ┃
//     ┃           ┃
//     ┃    ┻      ┃
//     ┃           ┃
//     ┗━┓       ┏━┛
//       ┃       ┃
//       ┃       ┃
//       ┃       ┗━━━┓
//       ┃           ┣┓
//       ┃           ┏┛
//       ┗┓┓┏━━━━━┳┓┏┛
//        ┃┫┫     ┃┫┫
//        ┗┻┛     ┗┻┛
//
// ━━━━━━感觉萌萌哒━━━━━━

// Author        : WhyWhy
// Created Time  : 2015年07月17日 星期五 20时49分42秒
// File Name     : 2492.cpp

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>

using namespace std;

const int MaxN=2010;

int map1[MaxN][MaxN];
int flag=0;
int vis[MaxN];
int N;
int que[MaxN],first,last;

bool bfs(int u)
{
    int v;

    first=last=0;
    que[last++]=u;
    vis[u]=1;

    while(last-first)
    {
        u=que[first++];

        for(v=1;v<=N;++v)
            if(map1[u][v]==flag && v!=u)
            {
                if(vis[v]==vis[u])
                    return 1;

                if(!vis[v])
                {
                    vis[v]=-vis[u];
                    que[last++]=v;
                }
            }
    }

    return 0;
}

bool getans()
{
    memset(vis,0,sizeof(vis));
    first=last=0;

    for(int i=1;i<=N;++i)
        if(!vis[i])
            if(bfs(i))
                return 1;

    return 0;
}

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);

    int T,cas=1;
    int Q;
    int a,b;

    scanf("%d",&T);

    while(T--)
    {
        scanf("%d %d",&N,&Q);
        ++flag;

        while(Q--)
        {
            scanf("%d %d",&a,&b);
            map1[a][b]=map1[b][a]=flag;
        }

        printf("Scenario #%d:
",cas++);

        if(getans())
            puts("Suspicious bugs found!
");
        else
            puts("No suspicious bugs found!
");
    }
    
    return 0;
}