hdu 1824 2-sat问题(判断)

/*
题意:u,v,w队长,队员,队长留下两个队员可以回家,两个队员留下,队长回家
2-sat问题,把两个队员看成一个整体就变成一个简单2-sat问题了
*/
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<stdlib.h>
using namespace std;
#define N  6100
#define NN 5100
struct node {
int u,v,w,next;
}bian[NN*8];
int head[N],yong,low[N],dfn[N],belong[N],ans,top,index,stac[N],vis[N];
void init()
{
    memset(head,-1,sizeof(head));
    yong=index=ans=top=0;
    memset(vis,0,sizeof(vis));
    memset(dfn,0,sizeof(dfn));
}
void addedge(int u,int v)
{
    bian[yong].v=v;
    bian[yong].next=head[u];
    head[u]=yong++;
}
void tarjan(int u)
{
    low[u]=dfn[u]=++index;
    stac[++top]=u;
    vis[u]=1;
    int i;
    for(i=head[u]; i!=-1; i=bian[i].next)
    {
        int v=bian[i].v;
        if(!dfn[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(vis[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        ans++;
        int t;
        do
        {
            t=stac[top--];
            belong[t]=ans;
            vis[t]=0;
        }
        while(t!=u);
    }
}
int slove(int n)
{
    int i;
    for(i=0; i<=n; i++)
        if(!dfn[i])
            tarjan(i);
    // printf("%d
",ans);
    for(i=0; i<=n; i+=2)
        if(belong[i]==belong[i+1])
            return 0;
    return 1;
}
int indx[N];
int main() {
    int n,m,i,u,len,v,w;
    while(scanf("%d%d",&n,&m)!=EOF) {
        init();
        len=-1;
        for(i=0;i<n;i++)  {
            scanf("%d%d%d",&u,&v,&w);
           indx[u]=++len;
           indx[v]=++len;
           indx[w]=len;
        }
        for(i=0;i<m;i++) {
            scanf("%d%d",&u,&v);
            addedge(indx[u],indx[v]^1);
            addedge(indx[v],indx[u]^1);
        }
        if(!slove(len))
            printf("no
");
        else
            printf("yes
");
    }
return 0;}

原文地址:https://www.cnblogs.com/thefirstfeeling/p/4410544.html