hdu 1824 Let's go home (2-sat)

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# include <stdio.h># include <algorithm># include <string.h># include <stack>using namespace std;# define MAXN  6010# define MAXM 10010struct node{    int to;    int next;} edge[MAXM];int tot;int tim,num;int be[MAXN];bool instack[MAXN];int dfn[MAXN],low[MAXN];int head[MAXN];int pos[MAXN];stack<int>s;int n,m;void init(){    tot=0;    memset(head,-1,sizeof(head));}void add(int from,int to){    edge[tot].to=to;    edge[tot].next=head[from];    head[from]=tot++;}void tarjan(int cur){    dfn[cur]=low[cur]=++tim;    s.push(cur);    instack[cur]=true;    for(int i=head[cur]; i!=-1; i=edge[i].next)    {        int to=edge[i].to;        if(!dfn[to])        {            tarjan(to);            low[cur]=min(low[cur],low[to]);        }        else if(instack[to])        {            low[cur]=min(low[cur],dfn[to]);        }    }    if(dfn[cur]==low[cur])    {        int tem = -1;        ++num;        while(tem != cur)        {            tem = s.top();            s.pop();            instack[tem] = false;            be[tem] = num;        }    }}void solve(){    memset(dfn,0,sizeof(dfn));    memset(low,0,sizeof(low));    memset(instack,0,sizeof(instack));    memset(be,0,sizeof(be));    while(!s.empty())        s.pop();    tim=num=0;    for(int i=0; i<2*n; i++)    {        if(!dfn[i])            tarjan(i);    }    bool ans=true;    for(int i=0; i<2*n; i++)    {        if(be[i]==be[i+n])        {            ans=false;            break;        }    }    if(ans)        puts("yes");    else        puts("no");}int main(){    int x,y,z;    while(~scanf("%d%d",&n,&m))    {        init();        for(int i=0; i<n; i++)        {            scanf("%d%d%d",&x,&y,&z);            pos[x]=i;            pos[y]=pos[z]=i+n;        }        for(int i=0; i<m; i++)        {            scanf("%d%d",&x,&y);            if(pos[x]>=n)                add(pos[x]-n,pos[y]);            else                add(pos[x]+n,pos[y]);            if(pos[y]>=n)                add(pos[y]-n,pos[x]);            else                add(pos[y]+n,pos[x]);        }        solve();    }    return 0;}
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