59 lines
1.4 KiB
C++
59 lines
1.4 KiB
C++
#include<iostream>
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#include<cstdio>
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#include<queue>
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#include<vector>
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#include<cstring>
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#include<map>
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#define MAX_V 110
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#define INF 0x7ffffff
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using namespace std;
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map <string,int> name;
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int ans[MAX_V][MAX_V],d[MAX_V][MAX_V],dd[MAX_V][MAX_V];
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bool ok[MAX_V][MAX_V];
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int main()
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{
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int n,m,a,b;
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while(~scanf("%d%d",&n,&m))
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{
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memset(d,0,sizeof(d));
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memset(ans,0,sizeof(ans));
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memset(ok,0,sizeof(ok));
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while(m--)
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{
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scanf("%d%d",&a,&b);
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ans[a][b]=ans[b][a]=d[a][b]=d[b][a]=1;
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ok[a][b]=ok[b][a]=1;
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}
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int times=6;
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while(times--){
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memset(dd,0,sizeof(dd));
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for(int i=0;i<n;i++){
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for(int j=0;j<n;j++){
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for(int k=0;k<n;k++){
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dd[i][j]+=ans[i][k]*d[k][j];
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}
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}
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}
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for(int i=0;i<n;i++){
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for(int j=0;j<n;j++){
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ans[i][j]=dd[i][j];
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}
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}
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for(int i=0;i<n;i++){
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for(int j=0;j<n;j++){
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if(ans[i][j]!=0) ok[i][j]=1;
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}
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}
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}
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int flag=1;
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for(int i=0;i<n;i++){
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for(int j=0;j<n;j++){
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if(ok[i][j]==0)
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flag=0;
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}
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}
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puts(flag?"Yes":"No");
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}
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return 0;
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}
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