「一本通 4.4 例 2」暗的连锁（loj10131）

思路：

　　诡异的树上倍增求LCA +　树上差分。。。　LCA模板敲错了，导致我改了好久好久。。。才改对

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
#include<vector>
#include<cstdlib>
#include<algorithm>
using namespace std;
const int maxn = 100010;
inline void qread(int &x){
    x = 0;
    register int ch = getchar();
    while(ch < '0' || ch > '9')    ch = getchar();
    while(ch >= '0' && ch <= '9'){
        x = 10 * x + ch - 48;
        ch = getchar();
    }
}
int n, m;
int deep[maxn];
int llog[maxn];
int f[maxn][25];
int val[maxn];
int g[maxn];
vector<int> G[maxn];
void dfs(int x){
    for(int i=0; i<G[x].size(); ++i){
        if(!deep[G[x][i]]){
            f[G[x][i]][0] = x;
            deep[G[x][i]] = deep[x] + 1;
            dfs(G[x][i]);
        }
    }
}
int LCA(int x, int y){
    if(deep[x] < deep[y])    swap(x, y);
        for(int k = llog[n]; k >= 0; k--){
            if(deep[f[x][k]] >= deep[y]){
                x = f[x][k];
            }
        }
    if(x != y){
        for(int k = llog[n]; k>=0; k--){
            if(f[x][k]!= f[y][k]){
                x = f[x][k];
                y = f[y][k];
            }
        }
        x = f[x][0];
    }
    return x;    
}
void dfs2(int x){
    for(int i=0; i<G[x].size(); ++i){
        if(G[x][i] != f[x][0]){
            dfs2(G[x][i]);
            val[x] += val[G[x][i]];
        }
    }
}
int main(void)
{
    srand(25426);
    qread(n);
    qread(m);
    for(int i=2; i<=n; ++i)    llog[i] = llog[i>>1] + 1;
    for(int i=1; i<n; ++i){
        int x, y;
        qread(x);
        qread(y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    int rt = rand() % n + 1;
    deep[rt] = 1;
    dfs(rt);
    for(int j=1; j<=llog[n]; ++j)
        for(int i=1; i <= n; ++i)
            f[i][j] = f[f[i][j-1]][j-1];
    for(int i=1; i<=m; ++i){
        int x, y;
        qread(x), qread(y);
        int a = LCA(x, y);
        val[x]++;
        val[y]++;
        val[a]-=2;
    }
    dfs2(rt);    
    int ans = 0;
    for(int i=1; i<=n; ++i){
        if(i==rt)    continue;
        if(val[i]==0){
            ans+=m;
        }else if(val[i] == 1){
            ans++;
        }
    }
    printf("%d\n", ans);
}