题目大意：

emmmmm

---

题解：

QAQ

---

#include <cstdio>

#include <cstring>

#include <iostream>

using namespace std;

#define ll long long

#define ri register int

#define rep(io, st, ed) for(ri io = st; io <= ed; io ++)

#define drep(io, ed, st) for(ri io = ed; io >= st; io --)

#define gc getchar

inline int read() {

	int p = 0, w = 1; char c = gc();

	while(c > '9' || c < '0') { if(c == '-') w = -1; c = gc(); }

	while(c >= '0' && c <= '9') p = p * 10 + c - '0', c = gc();

	return p * w;

}

const int sid = 5e5 + 5;

const ll inf = 1e17;

char mm[50];

int n, m, id, cnp, tim;

int ls[sid], rs[sid], rt[sid];

int cap[sid], nxt[sid], node[sid];

int sz[sid], son[sid], fa[sid], anc[sid];

int dfn[sid], ind[sid], L[sid], V[sid];

ll g[sid][2];

struct Mar {

	ll dp[2][2];

	inline ll* operator [] (const int x) { return dp[x]; }

} F[sid];

inline void addedge(int u, int v) {

	nxt[++ cnp] = cap[u]; cap[u] = cnp; node[cnp] = v;

}

#define cur node[i]

inline void dfs(int o) {

	sz[o] = 1;

	for(int i = cap[o]; i; i = nxt[i])

		if(cur != fa[o]) {

			fa[cur] = o; dfs(cur);

			sz[o] += sz[cur];

			if(sz[cur] > sz[son[o]]) son[o] = cur;

		}

}

inline void dfs(int o, int ac) {

	anc[o] = ac; L[ac] ++;

	dfn[o] = ++ tim; ind[tim] = o;

	if(!son[o]) return; dfs(son[o], ac);

	for(int i = cap[o]; i; i = nxt[i])

		if(cur != fa[o] && cur != son[o])

			dfs(cur, cur);

}

inline void upd(int o) {

	int lc = ls[o], rc = rs[o];

	F[o][0][0] = min(F[rc][0][0] + F[lc][0][0], F[rc][0][1] + F[lc][1][0]);

	F[o][0][1] = min(F[rc][0][0] + F[lc][0][1], F[rc][0][1] + F[lc][1][1]);

	F[o][1][0] = min(F[rc][1][0] + F[lc][0][0], F[rc][1][1] + F[lc][1][0]);

	F[o][1][1] = min(F[rc][1][0] + F[lc][0][1], F[rc][1][1] + F[lc][1][1]);

}

inline void build(int &o, int l, int r) {

	o = ++ id;

	if(l == r) {

		int u = ind[l];

		F[o][0][0] = F[o][1][0] = g[u][1];

		F[o][0][1] = g[u][0];

		F[o][1][1] = inf;

		return;

	}

	int mid = (l + r) >> 1;

	build(ls[o], l, mid);

	build(rs[o], mid + 1, r);

	upd(o);

}

inline void mdf(int o, int l, int r, int p) {

	if(l == r) {

		int u = ind[l];

		F[o][0][0] = F[o][1][0] = g[u][1];

		F[o][0][1] = g[u][0];

		F[o][1][1] = inf;

		return;

	}

	int mid = (l + r) >> 1;

	if(p <= mid) mdf(ls[o], l, mid, p);

	else mdf(rs[o], mid + 1, r, p);

	upd(o);

}

inline void build(int o) {

	int leaf = 0;

	g[o][0] = 0; g[o][1] = V[o];

	for(int i = cap[o]; i; i = nxt[i])

		if(cur != fa[o]) {

			leaf = 1; build(cur);

			if(cur == son[o]) continue;

			g[o][0] += F[rt[cur]][0][0];

			g[o][1] += min(F[rt[cur]][0][0], F[rt[cur]][0][1]);

		}

	if(anc[o] == o)

		build(rt[o], dfn[o], dfn[o] + L[o] - 1);

}

inline void mdf(int o, int opt, int nx) {

	int now = anc[o], up = fa[now], lst = o;

	if(opt == 1) g[o][0] += inf * nx;

	else g[o][1] += inf * nx;

	while(lst) {

		g[up][0] -= F[rt[now]][0][0];

		g[up][1] -= min(F[rt[now]][0][0], F[rt[now]][0][1]);

		mdf(rt[now], dfn[now], dfn[now] + L[now] - 1, dfn[lst]);

		g[up][0] += F[rt[now]][0][0];

		g[up][1] += min(F[rt[now]][0][0], F[rt[now]][0][1]);

		lst = up; now = anc[up]; up = fa[now];

	}

}

inline void solve() {

	int a = read(), x = read(), b = read(), y = read();

	mdf(a, x, 1); mdf(b, y, 1);

	ll ans = min(F[rt[1]][0][0], F[rt[1]][0][1]);

	ans = min(F[rt[1]][0][0], F[rt[1]][0][1]);

	if(ans >= 1e15) printf("-1\n");

	else printf("%lld\n", ans);

	mdf(a, x, -1); mdf(b, y, -1);

}

int main() {

	n = read(); m = read(); scanf("%s", mm + 1);

	rep(i, 1, n) V[i] = read();

	rep(i, 2, n) {

		int u = read(), v = read();

		addedge(u, v); addedge(v, u);

	}

	dfs(1);

	dfs(1, 1);

	build(1);

	rep(i, 1, m) solve();

	return 0;

}

大家都会写的题，不是吗？