rt 代码如下:

#include <cstdio>
#include <cctype>
#include <cmath>

using namespace std;

#define ll long long 

inline int read(){
    int res = 0, pdf = 0; char ch = getchar();
    while(!isdigit(ch)) pdf = ch == '-', ch = getchar();
    while(isdigit(ch)) res = (res<<3) + (res<<1) + (ch^48), ch = getchar();
    return pdf ? -res : res;
} 

inline void Print(ll x) {
	if (x < 0) x = -x, putchar('-'); 
	if (x < 10) putchar(x + '0'); 
	else {
		Print(x / 10); 
		putchar(x % 10 + '0'); 
	}
} 

inline void Swap(int &x, int &y) { int tmp = x; x = y; y = tmp; }

ll ans; 
const int N = 1e5 + 100, M = log2(N) + 5; 
int n, m; 
int head[N], nex[N << 1], ver[N << 1], val[N << 1], tot = 1; 
int vv[N], fa[N][M], depth[N], pre[N]; 

void Addedge(int x, int y) {
	ver[++tot] = y; 
	nex[tot] = head[x]; 
	head[x] = tot; 
}

void ins(int x, int fat) {
	fa[x][0] = fat; depth[x] = depth[fat] + 1; 
	for (int i = 1; i < M; ++i) {
		fa[x][i] = fa[fa[x][i - 1]][i - 1]; 
	}
	for (int i = head[x]; i; i = nex[i]) {
		int y = ver[i]; 
		if (y == fat) continue; 
		ins(y, x); 
	}
}

int lca(int x, int y) {
	if (depth[x] > depth[y]) Swap(x, y); 
	while (depth[x] < depth[y]) {
		int p = log2(depth[y] - depth[x]); 
		y = fa[y][p];
	}
	if (x == y) return x; 
	for (int i = M - 1; i >= 0; --i) {
		if (fa[x][i] != fa[y][i]) {
			x = fa[x][i];
			y = fa[y][i]; 
		}
	}
	return fa[x][0]; 
}

void dfs(int x, int fat) {
	pre[x] = vv[x]; 
	for (int i = head[x]; i; i = nex[i]) {
		int y = ver[i]; 
		if (y == fat) continue; 
		dfs(y, x); 
		pre[x] += vv[y]; 
	}
}

int main() {
	n = read(); m = read(); 
	int xx, yy; 
	for (int i = 1; i < n; ++i) {
		xx = read(); yy = read(); 
		Addedge(xx, yy); Addedge(yy, xx); 
	}
	ins(1, 0); 
	for (int i = 1; i <= m; ++i) {
		xx = read(); yy = read(); 
		++vv[xx]; ++vv[yy]; vv[lca(xx, yy)] -= 2; 
	} 
	dfs(1, 0); 
	for (int i = 1; i <= n; ++i) {
		if (!pre[i]) ans += (ll)(m); 
		else if (pre[i] == 1) ++ans;
	} 
	Print(ans); 
	return 0; 
}

救救孩子吧awa