hdu5452 Minimum Cut

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=5452

题意：给你一个图和它的生成树，要你在树上删一条边，问你最少删多少条边使得图不联通（开始时图一定联通）

解：

对每一条非树边对它两点之间的树上链的边+1，答案就是树上边的最小边权+1。处理上开始用了树状数组=TLE，其实由于只查询一次，用数组维护一下就好

/*
 * Problem:  
 * Author:  SHJWUDP
 * Created Time:  2015/9/23 星期三 19:32:28
 * File Name: 1001.cpp
 * State: 
 * Memo: 
 */
#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <algorithm>

using namespace std;

struct Graph {
    struct Edge {
        int u, v;
    };
    int n, m;
    vector<Edge> edges;
    vector<vector<int>> G;
    Graph(int _n):n(_n), G(_n){}
    void addEdge(int u, int v) {
        edges.push_back({u, v});
        m=edges.size();
        G[u].push_back(m-1);
    }
    vector<int>& operator[](int x) {
        return G[x];
    }
};

struct LinkCutTree {
    Graph G;
    vector<int> fa, siz, son, dep, top;
    vector<int> w;
    int id;
    vector<int> ans;
    LinkCutTree(int n):G(n){}
    void init() {
        fa.resize(G.n);
        siz.resize(G.n);
        son.resize(G.n);
        dep.resize(G.n);
        top.resize(G.n);
        w.resize(G.n);
        id=0;

        int root=1;
        fa[root]=-1;
        dfs1(root, 0);
        dfs2(root, root);
        ans.assign(G.n+7, 0);
    }
    int dfs1(int u, int d) {
        siz[u]=1; dep[u]=d; son[u]=-1;
        for(auto i : G[u]) {
            const auto& e=G.edges[i];
            if(e.v==fa[u]) continue;
            fa[e.v]=u;
            siz[u]+=dfs1(e.v, d+1);
            if(son[u]==-1 || siz[son[u]]<siz[e.v]) son[u]=e.v;
        }
        return siz[u];
    }
    void dfs2(int u, int tp) {
        w[u]=id++; top[u]=tp;
        if(son[u]!=-1) dfs2(son[u], tp);
        for(auto i : G[u]) {
            const auto & e=G.edges[i];
            if(e.v==fa[u] || e.v==son[u]) continue;
            dfs2(e.v, e.v);
        }
    }
    void update(int u, int  v) {
        int f1=top[u], f2=top[v];
        while(f1!=f2) {
            if(dep[f1]<dep[f2]) swap(f1, f2), swap(u, v);
    //        cout<<"\tup: "<<w[f1]<<"\t"<<w[u]+1<<endl;
            ++ans[w[f1]]; --ans[w[u]+1];
            u=fa[f1]; f1=top[u];
        }
        if(u==v) return;
        if(dep[u]>dep[v]) swap(u, v);
    //        cout<<"\tup: "<<w[u]<<"\t"<<w[v]<<endl;
        ++ans[w[son[u]]]; --ans[w[v]+1];
    }
};

int n, m;
int main() {
#ifndef ONLINE_JUDGE
    freopen("in", "r", stdin);
    //freopen("out", "w", stdout);
#endif
    int T, now=0;
    scanf("%d", &T);
    while(T--) {
        scanf("%d%d", &n, &m);
        LinkCutTree lct(n+1);
        Graph & G=lct.G;
        for(int i=0; i<n-1; ++i) {
            int a, b;
            scanf("%d%d", &a, &b);
            G.addEdge(a, b);
            G.addEdge(b, a);
        }
        lct.init();
        for(int i=n-1; i<m; ++i) {
            int a, b;
            scanf("%d%d", &a, &b);
            lct.update(a, b);
        }
        int ans=0x7f7f7f7f;
        for(int i=1; i<n; ++i) {
            lct.ans[i]+=lct.ans[i-1];
            ans=min(ans, lct.ans[i]);
        }
        printf("Case #%d: %d\n", ++now, ans+1);
    }
    return 0;
}