105 lines
2.1 KiB
C++
105 lines
2.1 KiB
C++
#include<stdio.h>
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#include<string.h>
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#include<stack>
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using namespace std;
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int n,m;
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struct edge_node
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{
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int to;
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int next;
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};
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edge_node edge[5000000];
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int head[100000];
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int dfn[100000];
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int low[100000];
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int visit[100000];
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int N;
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stack<int>sta;
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void tarjan_bfs(int cur,int time)
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{
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visit[cur]=1;
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visit[cur^1]=1;
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low[cur]=dfn[cur]=time;
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sta.push(cur);
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for(int i=head[cur];i!=-1;i=edge[i].next)
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{
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if(visit[edge[i].to]==0)
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{
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tarjan_bfs(edge[i].to,time++);
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time++;
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}
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if(visit[edge[i].to]==1&&low[cur]>low[edge[i].to])
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{
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low[cur]=low[edge[i].to];
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}
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}
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if(dfn[cur]==low[cur])
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{
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N++;
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while(!sta.empty()&&sta.top()!=cur)
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{
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low[sta.top()]=N;
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visit[sta.top()]=2;
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sta.pop();
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}
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}
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return;
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}
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void tarjan()
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{
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N=0;
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memset(dfn,0,sizeof(dfn));
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memset(low,0,sizeof(low));
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memset(visit,0,sizeof(visit));
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for(int i=0;i<2*n;i++)
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{
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if(visit[i]==0)
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{
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tarjan_bfs(i,1);
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}
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}
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return;
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}
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int main()
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{
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while(scanf("%d%d",&n,&m)!=EOF)
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{
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memset(head,-1,sizeof(head));
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int counter=0;
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while(m--)
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{
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int a1,a2,c1,c2;
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scanf("%d%d%d%d",&a1,&a2,&c1,&c2);
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int temp1;
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int temp2;
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temp1=2*a1+c1;
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temp2=2*a2+c2;
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edge[counter].to=temp2;
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edge[counter].next=head[temp1^1];
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head[temp1^1]=counter++;
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edge[counter].to=temp1;
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edge[counter].next=head[temp2^1];
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head[temp2^1]=counter++;
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}
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tarjan();
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int sign=1;
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for(int i=0;i<2*n;i++)
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{
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if(low[i]==low[i^1])
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{
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sign=0;
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break;
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}
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}
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if(sign==1)
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{
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printf("YES\n");
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}
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else
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{
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printf("NO\n");
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}
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}
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return 0;
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}
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