[POJ3648 Wedding]

[关键字]：2-sat

[题目大意]：http://poj.org/problem?id=3648

//=====================================================================================================

[分析]：http://blog.csdn.net/l04205613/article/details/6673512这个博客对于2-sat的题目总结的不错。

[代码]：

View Code

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<vector>
using namespace std;

int n,m,sum,top;
int c[5100],s[5100],colour[5100];
bool v[5100];
vector<int> e[5100],re[5100],dag[5100];

int pre()
{
    for (int i=0;i<5010;i++) {e[i].clear();re[i].clear();dag[i].clear();}
    return 0;
}

int cal(int x,char ch)
{
    int res=x*2;
    if (ch=='h') return res; else return res+1;
}

int dfs1(int u)
{
    v[u]=1;
    int size=e[u].size();
    for (int i=0;i<size;i++) 
    {
        int temp=e[u][i];
        if (!v[temp]) dfs1(temp);
    }
    s[++top]=u;
    return 0;
}

int dfs2(int u)
{
    v[u]=1;
    int size=re[u].size();
    for (int i=0;i<size;i++)
    {
        int temp=re[u][i];
        if (!v[temp]) dfs2(temp);
    }
    c[u]=sum;
    return 0;
}

int kosaraju()
{
    sum=top=0;
    memset(v,0,sizeof(v));
    for (int i=0;i<2*n;i++)
        if (!v[i]) dfs1(i);
    memset(v,0,sizeof(v));
    for (int i=2*n;i;i--)
        if (!v[s[i]]) sum++,dfs2(s[i]);
    for (int i=0;i<2*n;i++)
    {
        int size=re[i].size();
        for (int j=0;j<size;j++)
        {
            int temp=re[i][j];
            if (c[i]!=c[temp]) dag[c[i]].push_back(c[temp]);
        }
    }
    return 0;
}

bool solveable()
{
     for (int i=0;i<2*n;i+=2)
         if (c[i]==c[i+1]) return 0;
     return 1;
}

int dfs(int u)
{
    colour[u]=2;
    int size=dag[u].size();
    for (int i=0;i<size;i++)
    {
        int temp=dag[u][i];
        if (!colour[temp]) dfs(temp);
    }
    return 0;
}

int solve()
{
    memset(colour,0,sizeof(colour));
    for (int i=sum;i;i--)
    {
        if (!colour[i])
        {
                       colour[i]=1;
                       for (int j=0;j<2*n;j++)
                           if (c[j]==i)
                           {
                                       int temp=c[j^1];
                                       if (!colour[temp]) dfs(temp);
                           }
        }
    }
    for (int i=2;i<2*n;i++)
        if (colour[c[i]]==colour[c[1]]) printf("%d%c ",i/2,i&1?'w':'h');
    printf("\n");
    return 0;
}

int main()
{
    while(~scanf("%d%d",&n,&m))
    {            
            getchar();
            if (!n && !m) break;
            int a,b,u,v;
            char ch1,ch2;
            pre();
            for (int i=0;i<m;i++)
            {
                scanf("%d%c%d%c",&a,&ch1,&b,&ch2);                
                getchar();
                u=cal(a,ch1),v=cal(b,ch2);
                e[u].push_back(v^1),e[v].push_back(u^1);
                re[v^1].push_back(u),re[u^1].push_back(v);
            }
            e[1].push_back(0),re[0].push_back(1);
            kosaraju();
            if (solveable()) solve(); else printf("bad luck\n");
    }
    return 0;
}