38 lines
1.3 KiB
C++
38 lines
1.3 KiB
C++
#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#define len 1000005
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int ans[len],head[len],next[len],val[len],degree[len],n,m;
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bool toposort(){
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int i,front,rear,u;
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for(i=rear=1;i<=n;i++)
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if(degree[i]==0)
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ans[rear++]=i;
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for(front=1;front<rear;front++){
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for(u=head[ans[front]];u;u=next[u])
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if(--degree[val[u]]==0)
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ans[rear++]=val[u];
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}
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if(rear==n+1) return true;
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else return false;
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}
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int main(void){
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int i,x,y,k;
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while(scanf("%d%d",&n,&m)==2&&m+n){
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memset(head,0,sizeof(head));
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memset(degree,0,sizeof(degree));
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for(i=k=1;i<=m;i++){
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scanf("%d%d",&x,&y);
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degree[y]++;
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val[k]=y;
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next[k]=head[x]; head[x]=k++;
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}
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if(toposort())
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for(i=1;i<=n;i++)
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printf("%d\n",ans[i]);
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else
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puts("IMPOSSIBLE");
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}
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return 0;
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}
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