街道赛跑 题解

题目在主页，如有出错请指出

include <bits/stdc++.h>

using namespace std;

int ans[55], ans2[55];
int vis[55], vis2[55];
vector < int > a[55];

void dfs(int x)
{
vis[x] = 1;
for (auto i : a[x])
if (vis[i] == 0) dfs(i);
}

void dfs2(int x)
{
vis2[x] = 1;
for (auto i : a[x])
if (vis2[i] == 0) dfs2(i);
}

int main()
{
int x, cnt = 0;
while (cin >> x)
{
if (x == -1) break;
if (x == -2)
{
cnt++;
continue;
}
a[cnt].push_back(x);
}
int n = --cnt;
cnt = 0;
for (int i = 1; i <= n - 1; i++)
{
memset(vis, 0, sizeof vis);
vis[i] = -1;
dfs(0);
if (vis[n] == 0) ans[++cnt] = i;
}
cout << cnt;
for (int i = 1; i <= cnt; i++)
cout << " " << ans[i];
cout << endl;

int total = 0;
for (int i = 1; i <= cnt; i++)
{
	memset(vis, 0, sizeof vis);
	vis[ans[i]]	= -1;
	dfs(0);
	memset(vis2, 0, sizeof vis2);
	dfs2(ans[i]);
	bool flag = 1;
	for (int j = 0; j <= n; j++)
	{
		if (vis[j] == 1 && vis2[j] == 1 ) 
		{
			flag = 0;
			break;	
		} 
	}
	if (flag) ans2[++total] = ans[i];
}	
cout << total;
for (int i = 1; i <= total; i++)
	cout << " " << ans2[i];
cout << endl; 
return 0;

}