BZOJ 1776: [Usaco2010 Hol]cowpol 奶牛政坛 LCA + 树的直径

Code:

#include <bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin)
#define maxn 300000
using namespace std;
vector<int>G[maxn];
int n,tot,root,edges;
int fa[maxn];
int hd[maxn],to[maxn],nex[maxn],top[maxn],dep[maxn],son[maxn],siz[maxn];
void addedge(int u,int v) {
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;
}
void dfs1(int u) {
    dep[u]=dep[fa[u]]+1, siz[u]=1;
    for(int i=hd[u];i;i=nex[i]) {
        int v=to[i];
        if(v==fa[u]) continue;
        dfs1(v), siz[u]+=siz[v];
        if(siz[v]>siz[son[u]]) son[u]=v;
    }
}
void dfs2(int u,int tp) {
    top[u]=tp;
    if(son[u]) dfs2(son[u], tp);
    for(int i=hd[u];i;i=nex[i]) {
        int v=to[i];
        if(v==fa[u]||v==son[u]) continue;
        dfs2(v,v);
    }
}
int LCA(int x,int y) {
    while(top[x]^top[y]) {
        dep[top[x]] > dep[top[y]] ? x = fa[top[x]] : y = fa[top[y]];
    }
    return dep[x]<dep[y]?x:y;
}
int main() {
    // setIO("input");
    scanf("%d%d",&n,&tot);
    for(int i=1;i<=n;++i) {
        int ty;
        scanf("%d%d",&ty,&fa[i]);
        if(!fa[i]) root=i;
        else addedge(fa[i],i);
        G[ty].push_back(i);
    }
    dfs1(root), dfs2(root,root);
    for(int i=1;i<=tot;++i) {
        int mx=0,ans=0;
        for(int j=0;j<G[i].size();++j) {
            if(dep[G[i][j]] > dep[mx]) mx = G[i][j];
        }
        for(int j=0;j<G[i].size();++j) {
            // printf("%d %d\n",mx,G[i][j]);
            ans=max(ans, dep[mx] + dep[G[i][j]] - (dep[LCA(mx, G[i][j])] << 1));
        }
        printf("%d\n",ans);
    }
    return 0;
}