USACO 4.3 Street Race(DFS)

/*
ID:cuizhe
LANG: C++
TASK: race3
*/
#include <cstdio>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <algorithm>
using namespace std;
#define INF 100000
int p[101][101];
int o[101];
int flag[101];
int n;
int dfs(int x)
{
int i;
if(x == n) return 1;
for(i = 0;i <= n;i ++)
{
if(p[x][i] == 1&&!o[i])
{
o[i] = 1;
if(dfs(i))
return 1;
o[i] = 0;
}
}
return 0;
}
void dfs1(int x,int key)
{
int i;
if(x == key) return;
for(i = 0;i <= n;i ++)
{
if(p[x][i] == 1&&!o[i])
{
o[i] = 1;
dfs1(i,key);
}
}
return ;
}
int dfs2(int x,int key)
{
int i;
if(x == key) return 0;
for(i = 0;i <= n;i ++)
{
if(p[x][i] == 1&&!o[i])
{
o[i] = 2;
if(dfs2(i,key))
return 1;
}
else if(p[x][i] == 1&&o[i] == 1)
{
return 1;
}
}
return 0;
}
int main()
{
int i,j,num,ans = 0;
freopen("race3.in","r",stdin);
freopen("race3.out","w",stdout);
for(i = 0;i <= 50;i ++)
{
for(j = 0;j <= 50;j ++)
p[i][j] = INF;
p[i][i] = 0;
}
for(i = 0;;i ++)
{
scanf("%d",&num);
if(num == -1) break;
if(num == -2) continue;
p[i][num] = 1;
for(;;)
{
scanf("%d",&num);
if(num == -2) break;
p[i][num] = 1;
}
}
n = i-1;
for(i = 1;i < n;i ++)
{
memset(o,0,sizeof(o));
o[i] = 1;
if(!dfs(0))
{
flag[i] = 1;
ans ++;
}
o[i] = 0;
}
printf("%d",ans);
for(i = 1;i < n;i ++)
{
if(flag[i]) printf(" %d",i);
}
printf("\n");
ans = 0;
for(i = 1;i < n;i ++)
{
if(flag[i])
{
memset(o,0,sizeof(o));
o[0] = 1;
dfs1(0,i);
o[i] = 2;
if(dfs2(i,n))
continue;
else
{
flag[i] = 2;
ans ++;
}
}
}
printf("%d",ans);
for(i = 1;i < n;i ++)
{
if(flag[i] == 2) printf(" %d",i);
}
printf("\n");
return 0;
}