ZOJ 2475 Benny's Compiler(DFS)

#include <iostream>
#include <cstdio>
#include <memory.h>
using namespace std;
const int maxn = 110;
int n, e;
bool g[maxn][maxn], vis[maxn];

bool dfs(int u){
vis[u] = 1;
for (int i = 1; i <= n; ++i){
if(g[u][i] && u != i){
if(vis[i])return false;
else{
vis[i] = 1;
if(!dfs(i)) return false;
vis[i] = 0;
}
}
}
return true;
}
int main(){
while (scanf("%d", &n) && n > 0){
memset(vis, 0, sizeof(vis));
memset(g, false, sizeof(g));
for (int i = 0; i < n; ++i){
int u, v;
scanf("%d %d", &u, &v);
g[u][v] = 1;
}
scanf("%d", &e);
if(dfs(e)){
printf("Yes\n");
}else{
printf("No\n");
}
}
return 0;
}