[BZOJ1823][JSOI2010]满汉全席 做题笔记

题目链接：http://www.lydsy.com/JudgeOnline/problem.php?id=1823

我做的第一道2-SAT裸题。不得不说题目描述看起来比NOI2002银河英雄传说都可怕。。。注意图是有向的。

#include <cstdio>#include <cstring>#include <algorithm>#include <stack>using namespace std;const int N=2005,M=20005,inf=0x3fffffff;int head[N],ver[M<<1],next[M<<1];int dfn[N],low[N],bel[N],q[N<<1],m,n,scc;bool inq[N];int tot=1,t=0,T,top=0;void add (int u,int v) {    ver[++tot]=v;next[tot]=head[u];head[u]=tot;}inline int read(){    int x=0,f=1;char ch=getchar();    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}    return x*f;}int get () {    int x;    char c=getchar();    while (c!='m'&&c!='h') c=getchar();    if (c=='m') x=read()*2;    else x=read()*2+1;    return  x;}void Tarjan (int x) {    dfn[x]=low[x]=++t;    q[++top]=x;inq[x]=1;    for (int i=head[x];i;i=next[i])         if (!dfn[ver[i]]) {            Tarjan(ver[i]);            low[x]=min(low[x],low[ver[i]]);        }        else if (inq[ver[i]])             low[x]=min(low[x],dfn[ver[i]]);    if (low[x]==dfn[x]) {        scc++;        int now=0;        while (now!=x) {            now=q[top--];            bel[now]=scc;            inq[now]=0;        }    }}int main () {    T=read();    while (T--) {        memset(head,0,sizeof(head));        memset(dfn,0,sizeof(dfn));        memset(low,0,sizeof(low));        memset(bel,0,sizeof(bel));        memset(inq,0,sizeof(inq));        tot=1,t=m=n=scc=top=0;        n=read(); m=read();        int x,y,xp,yp;        for (int i=1;i<=m;i++) {            x=get(); y=get();            xp=x^1;yp=y^1;            add(xp,y);add(yp,x);        }        bool flag=0;        for (int i=2;i<=2*n+1;i++)             if (!dfn[i]) Tarjan(i);        for (int i=1;i<=n;i++)             if (bel[2*i]==bel[2*i+1])                 { puts("BAD");flag=1;break; }        if (!flag) puts("GOOD");    }    return 0;}