Problem:
Do use segment tree

Given a tree with n (1 ≤ n ≤ 200,000) nodes and a list of q (1 ≤ q ≤ 100,000) queries,
process the queries in order and output a value for each output query.
The given tree is connected and each node on the tree has a weight wi (-10,000 ≤ wi ≤ 10,000).

Each query consists of a number ti (ti = 1, 2), which indicates the type of the query , and three numbers ai, bi and ci (1 ≤ ai, bi ≤ n, -10,000 ≤ ci ≤ 10,000).
Depending on the query type, process one of the followings:

(ti = 1: modification query)
Change the weights of all nodes on the shortest path between ai and bi (both inclusive) to ci.

(ti = 2: output query)
First, create a list of weights on the shortest path between ai and bi (both inclusive) in order. After that, output the maximum sum of a non-empty continuous subsequence of the weights on the list. ci is ignored for output queries.

Input

The first line contains two integers n and q.
On the second line, there are n integers which indicate w1, w2, ... , wn.

Each of the following n - 1 lines consists of two integers si and ei (1 ≤ si, ei ≤ n),
which means that there is an edge between si and ei.

Finally the following q lines give the list of queries, each of which contains four integers in the format described above.
Queries must be processed one by one from top to bottom.

Output

For each output query, output the maximum sum in one line.

Sample Input 1

3 4
1 2 3
1 2
2 3
2 1 3 0
1 2 2 -4
2 1 3 0
2 2 2 0

Output for the Sample Input 1

6
3
-4

Sample Input 2

7 5
-8 5 5 5 5 5 5
1 2
2 3
1 4
4 5
1 6
6 7
2 3 7 0
2 5 2 0
2 4 3 0
1 1 1 -1
2 3 7 0

Output for the Sample Input 2

12
10
10
19

Sample Input 3

21 30
10 0 -10 -8 5 -5 -4 -3 1 -2 8 -1 -7 2 7 6 -9 -6 3 4 9
10 3
3 2
3 12
12 4
4 13
4 9
10 21
21 1
1 11
11 14
1 15
10 6
6 17
6 16
6 5
5 18
5 19
10 7
10 8
8 20
1 1 21 -10
1 3 19 10
2 1 13 0
1 4 18 8
1 5 17 -5
2 16 7 0
1 6 16 5
1 7 15 4
2 4 20 0
1 8 14 3
1 9 13 -1
2 9 18 0
1 10 12 2
1 11 11 -8
2 21 15 0
1 12 10 1
1 13 9 7
2 6 14 0
1 14 8 -2
1 15 7 -7
2 10 2 0
1 16 6 -6
1 17 5 9
2 12 17 0
1 18 4 6
1 19 3 -3
2 11 8 0
1 20 2 -4
1 21 1 -9
2 5 19 0

Output for the Sample Input 3

20
9
29
27
10
12
1
18
-2
-3

Solution in C++14 (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using graph = vector<vector<int>>;

struct RMS {
	static const int INF = 1e9 + 1000;
	struct type {
		int left, right, all, sum;
		type() : left(-INF), right(-INF), all(-INF), sum(0) {}
		type(int val) : left(val), right(val), all(val), sum(val) {}
		type(int l, int r, int a, int s) : left(l), right(r), all(a), sum(s) {}
	};
	static type id() { return type(); }
	static type op(const type& l, const type & r) {
		return type(max(l.left, l.sum + r.left), max(r.right, r.sum + l.right), max({ l.all, r.all, l.right + r.left }), l.sum + r.sum);
	}
};

class lct_node {
	using M = RMS;
	using T = typename M::type;
	using U = int;

	lct_node *l, *r, *p;
	bool rev;
	T val, all;
	int size;
	bool flag;
	U lazy;

	int pos() {
		if (p && p->l == this) return -1;
		if (p && p->r == this) return 1;
		return 0;
	}
	void update() {	// * fix
		size = (l ? l->size : 0) + (r ? r->size : 0) + 1;
		all = M::op(l ? l->all : M::id(), M::op(val, r ? r->all : M::id()));
	}
	void update_lazy(U v) {	// * fix
		val = T(v);
		all = v > 0 ? T(v * size) : T(v, v, v, v * size);
		lazy = v;
		flag = true;
	}
	void rev_data() {	// * fix
		swap(val.left, val.right);
		swap(all.left, all.right);
	}
	void push() {
		if (pos()) p->push();
		if (rev) {
			swap(l, r);
			if (l) l->rev ^= true, l->rev_data();
			if (r) r->rev ^= true, r->rev_data();
			rev = false;
		}
		if (flag) {
			if (l) l->update_lazy(lazy);
			if (r) r->update_lazy(lazy);
			flag = false;
		}
	}
	void rot() {
		lct_node *par = p;
		lct_node *mid;
		if (p->l == this) {
			mid = r;
			r = par;
			par->l = mid;
		}
		else {
			mid = l;
			l = par;
			par->r = mid;
		}
		if (mid) mid->p = par;
		p = par->p;
		par->p = this;
		if (p && p->l == par) p->l = this;
		if (p && p->r == par) p->r = this;
		par->update();
		update();
	}
	void splay() {
		push();
		while (pos()) {
			int st = pos() * p->pos();
			if (!st) rot();
			else if (st == 1) p->rot(), rot();
			else rot(), rot();
		}
	}

public:
	lct_node() : l(nullptr), r(nullptr), p(nullptr), rev(false), val(M::id()), all(M::id()), size(1), flag(false) {}
	lct_node(const T& v) : l(nullptr), r(nullptr), p(nullptr), rev(false), val(v), all(v), size(1), flag(false) {}
	void init(U v) {
		val = all = T(v);
	}
	void expose() {
		for (lct_node *x = this, *y = nullptr; x; y = x, x = x->p) x->splay(), x->r = y, x->update();
		splay();
	}
	void link(lct_node *x) {
		x->expose();
		expose();
		p = x;
	}
	void cut() {
		expose();
		l->p = nullptr;
		l = nullptr;
		update();
	}
	void evert() {
		expose();
		rev = true;
		rev_data();
	}
	T find() {
		expose();
		return all;
	}
	void update(U v) {
		expose();
		update_lazy(v);
	}
};

const int MAX = 2e5;

lct_node lct[MAX];
int w[MAX];

void build(int v, int prev, const graph& G) {
	lct[v].init(w[v]);
	for (auto to : G[v]) if (to != prev) {
		build(to, v, G);
		lct[to].link(&lct[v]);
	}
}

int main()
{
	ios::sync_with_stdio(false), cin.tie(0);
	int N, Q;
	cin >> N >> Q;
	for (int i = 0; i < N; i++) {
		cin >> w[i];
	}
	graph G(N);
	for (int i = 0; i < N - 1; i++) {
		int u, v;
		cin >> u >> v; u--, v--;
		G[u].push_back(v);
		G[v].push_back(u);
	}
	build(0, -1, G);
	while (Q--) {
		int t, a, b, c;
		cin >> t >> a >> b >> c; a--, b--;
		if (t == 1) {
			lct[a].evert();
			lct[b].update(c);
		}
		else {
			lct[a].evert();
			printf("%d\n", (int)lct[b].find().all);
		}
	}
	return 0;
}