Submission #1690045

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Source Code Expand

#include<bits/stdc++.h>
#define N 200009
using namespace std;

int n,rt,last,a[N],fa[N],fst[N],nxt[N],tg[N],f[N],g[N],bo[N];
void dfs(int x){
	int y;
	for (y=fst[x]; y; y=nxt[y]) if (!bo[y]) dfs(y);
	for (y=fst[x]; y; y=nxt[y]) if (!bo[y]) tg[f[y]]=x;
	for (y=0; tg[y]==x; y++);
	f[x]=y;
	for (y++; tg[y]==x; y++);
	g[x]=y;
}
int main(){
	scanf("%d",&n);
	int i;
	for (i=1; i<=n; i++){
		scanf("%d",&fa[i]);
		nxt[i]=fst[fa[i]]; fst[fa[i]]=i;
	}
	for (i=1; !bo[i]; i=fa[i]) bo[i]=1;
	memset(bo,0,sizeof(bo));
	for (; !bo[i]; i=fa[i]) bo[i]=1;
	rt=last=i;
	for (; bo[i]==1; last=i,i=fa[i]){ dfs(i); bo[i]=2; }
	for (a[rt]=f[rt],i=rt; fa[i]!=rt; i=fa[i])
		a[fa[i]]=(a[i]==f[fa[i]]?g[fa[i]]:f[fa[i]]);
	if (a[last]!=a[rt]){
		puts("POSSIBLE"); return 0;
	}
	for (a[rt]=g[rt],i=rt; fa[i]!=rt; i=fa[i])
		a[fa[i]]=(a[i]==f[fa[i]]?g[fa[i]]:f[fa[i]]);
	puts(a[last]==f[rt]?"POSSIBLE":"IMPOSSIBLE");
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:16:16: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
                ^
./Main.cpp:19:21: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&fa[i]);
                     ^

Judge Result