CodeForces 116C 【BFS】

思路：

求所有树的最大高度？

注意：所有树从树根开始？

#include <bits/stdc++.h>using namespace std;typedef long long LL;struct asd{int to;int next;}e[2500];int head[2500],tol;int pre[2500];int n;void add(int u,int v){e[tol].to=v;e[tol].next=head[u];head[u]=tol++;}bool vis[2500];struct ad{int w;int step;};int BFS(int s){int res=0;vis[s]=1;ad now,nex;now.step=1;now.w=s;queue<ad>q;q.push(now);while(!q.empty()){now=q.front();q.pop();res=max(now.step,res);int u=now.w;for(int i=head[u];~i;i=e[i].next){int v=e[i].to;if(vis[v]) continue;vis[v]=1;nex.w=v;nex.step=now.step+1;q.push(nex);}}return res;}int main(){int x;scanf("%d",&n);tol=0;memset(head,-1,sizeof(head));memset(vis,0,sizeof(vis));memset(pre,0,sizeof(pre));for(int i=1;i<=n;i++){scanf("%d",&x);if(x==-1) continue;add(x,i);pre[i]++;}int ans=0;for(int i=1;i<=n;i++){if(!pre[i]){ans=max(ans,BFS(i));}}printf("%d\n",ans);return 0;}