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-);
     }
     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=;

         int root=;
         fa[root]=-;
         dfs1(root, );
         dfs2(root, root);
         ans.assign(G.n+, );
     }
     int dfs1(int u, int d) {
         siz[u]=; dep[u]=d; son[u]=-;
         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+);
             if(son[u]==- || 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]!=-) 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]+];
             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]+];
     }
 };

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