【LCA】 POJ 3417 Network 记数

mark 明天再写

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <string>
#include <iostream>
#include <algorithm>
#include <sstream>
#include <cmath>
using namespace std;
#include <queue>
#include <stack>
#include <vector>
#include <deque>
#define cler(arr, val)    memset(arr, val, sizeof(arr))
#define FOR(i,a,b)  for(int i=a;i<=b;i++)
#define IN   freopen ("in.txt" , "r" , stdin);
#define OUT  freopen ("out.txt" , "w" , stdout);
typedef long long  LL;
const int MAXN = 100000+5;
const int MAXM = 200000;
const int INF = 0x3f3f3f3f;
const int mod = 1000000007;
const double eps= 1e-8;
int rmq[2*MAXN];//rmq数组，就是欧拉序列对应的深度序列
struct ST
{
    int mm[2*MAXN];
    int dp[2*MAXN][20];//最小值对应的下标
    void init(int n)
    {
        mm[0] = -1;
        for(int i = 1; i <= n; i++)
        {
            mm[i] = ((i&(i-1)) == 0)?mm[i-1]+1:mm[i-1];
            dp[i][0] = i;
        }
        for(int j = 1; j <= mm[n]; j++)
            for(int i = 1; i + (1<<j)  - 1 <= n; i++)
                dp[i][j] = rmq[dp[i][j-1]] <
                           rmq[dp[i+(1<<(j-1))][j-1]]?dp[i][j-1]:dp[i+(1<<(j-1))][j-1];
    }
    int query(int  a,int b)//查询[a,b]之间最小值的下标
    {
        if(a > b)swap(a,b);
        int k = mm[b-a+1];
        return rmq[dp[a][k]] <=
               rmq[dp[b-(1<<k)+1][k]]?dp[a][k]:dp[b-(1<<k)+1][k];
    }
};
//边的结构体定义
struct Edge
{
    int to,next;
};
Edge edge[MAXM];
int tot,head[MAXN],num[MAXN];
int F[MAXN*2];//欧拉序列，就是dfs遍历的顺序，长度为2*n-1,下标从1开始
int P[MAXN];//P[i]表示点i在F中第一次出现的位置
int cnt;
ST st;
void init()
{
    tot = 0;
    memset(head,-1,sizeof (head));
    memset(num,0,sizeof (num));

}
void addedge(int  u,int  v)//加边，无向边需要加两次
{
    edge[tot].to = v;
    edge[tot].next = head[u];
    head[u] = tot++;
}
void dfs(int u,int pre,int dep)
{
    F[++cnt] = u;
    rmq[cnt] = dep;
    P[u] = cnt;
    for(int i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].to;
        if(v == pre) continue;
        dfs(v,u,dep+1);
        F[++cnt] = u;
        rmq[cnt] = dep;
    }
}
void LCA_init(int  root,int  node_num)//查询LCA前的初始化
{
    cnt = 0;
    dfs(root,root,0);
    st.init(2*node_num-1);
}
int query_lca(int  u,int v)//查询u,v的lca编号
{
    return F[st.query(P[u],P[v])];
}
void dp(int u,int pre)
{
    for(int i=head[u];~i;i=edge[i].next)
    {
        int v=edge[i].to;
        if(v!=pre)
        {
            dp(v,u);
            num[u]+=num[v];
        }
    }
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
#endif
    int n,m,u,v;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        init();
        for(int i=0;i<n-1;i++)
        {
            scanf("%d%d",&u,&v);
            addedge(u,v);
            addedge(v,u);
        }
        LCA_init(1,n);
        for(int i=0;i<m;i++)
        {
            scanf("%d%d",&u,&v);
            num[u]++,num[v]++;
            num[query_lca(u,v)]-=2;
        }
        dp(1,0);
        int ans=0;
        for(int i=2;i<=n;i++)
        {
            if(num[i]==0) ans+=m;
            else if(num[i]==1) ans++;
        }
        cout<<ans<<endl;
    }
    return 0;
}