67 lines
1.3 KiB
C++
67 lines
1.3 KiB
C++
#include<stdio.h>
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#include<string.h>
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struct A
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{
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int ts;
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int outdegree;
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int total;
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int mem[15];
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}E[10011];
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int max(int a,int b)
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{
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return a>b?a:b;
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}
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int topsort(int n)
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{
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int k,i,j;
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int flag;
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int temp;
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k=0;
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while(k<n)
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{
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flag=0;
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for(i=1;i<=n;i++)
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{
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if(E[i].outdegree==0)
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{
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E[i].outdegree--;
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temp=E[i].ts+1;
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for(j=0;j<E[i].total;j++)
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{
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E[E[i].mem[j]].outdegree--;
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E[E[i].mem[j]].ts=max(temp,E[E[i].mem[j]].ts);
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}
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flag=1;
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k++;
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}
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}
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if(flag==0) return 1;
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}
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return 0;
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}
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int main()
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{
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int n,m;
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int i;
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int a,b;
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int flag;
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int ans;
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while(scanf("%d%d",&n,&m)!=-1)
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{
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for(i=1;i<=n;i++) E[i].ts=E[i].total=E[i].outdegree=0;
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while(m--)
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{
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scanf("%d%d",&a,&b);
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E[a].outdegree++;
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E[b].mem[E[b].total++]=a;
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}
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flag=topsort(n);
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if(flag) {printf("-1\n");continue;}
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ans=0;
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for(i=1;i<=n;i++) ans+=E[i].ts;
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ans+=888*n;
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printf("%d\n",ans);
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}
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return 0;
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}
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