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++11 (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
using Int = long long;


template<typename T,typename E>
struct LinkCutTree{
  struct Node{
    Node *l,*r,*p;
    size_t cnt;
    int idx;
    bool rev;
    T val,dat;
    E laz;
    Node():cnt(0){}
    Node(int idx,T val,E laz):
      cnt(1),idx(idx),rev(0),val(val),dat(val),laz(laz){l=r=p=nullptr;}
    bool is_root(){
      return !p||(p->l!=this&&p->r!=this);
    }
  };
  
  using F = function<T(T,T)>;
  using G = function<T(T,E)>;
  using H = function<E(E,E)>;
  using P = function<E(E,size_t)>;
  F f;
  G g;
  H h;
  P p;
  T ti;
  E ei;
  
  const size_t LIM = 1e6;
  vector<Node> pool;
  size_t ptr;
  
  LinkCutTree(F f,G g,H h,P p,T ti,E ei):
    f(f),g(g),h(h),p(p),ti(ti),ei(ei),pool(LIM),ptr(0){}
  
  inline Node* create(){
    return &pool[ptr++];
  }
  
  inline Node* create(int idx,T v){
    return &(pool[ptr++]=Node(idx,v,ei));
  }

  void propagate(Node *t,E v){
    t->laz=h(t->laz,v);
    t->val=g(t->val,v);
    t->dat=g(t->dat,p(v,t->cnt));
  }

  void toggle(Node *t){
    swap(t->l,t->r);
    t->rev^=1;
  }

  void eval(Node *t){
    if(t->laz!=ei){
      if(t->l) propagate(t->l,t->laz);
      if(t->r) propagate(t->r,t->laz);
      t->laz=ei;
    }
    if(t->rev){
      if(t->l) toggle(t->l);
      if(t->r) toggle(t->r);
      t->rev=false;
    }
  }

  void update(Node *t){
    t->cnt=1;
    t->dat=t->val;
    if(t->l) t->cnt+=t->l->cnt,t->dat=f(t->l->dat,t->dat);
    if(t->r) t->cnt+=t->r->cnt,t->dat=f(t->dat,t->r->dat);
  }

  void rotR(Node *t){
    Node *x=t->p,*y=x->p;
    if((x->l=t->r)) t->r->p=x;
    t->r=x;x->p=t;
    update(x);update(t);
    if((t->p=y)){
      if(y->l==x) y->l=t;
      if(y->r==x) y->r=t;
      update(y);
    }
  }
  
  void rotL(Node *t){
    Node *x=t->p,*y=x->p;
    if((x->r=t->l)) t->l->p=x;
    t->l=x;x->p=t;
    update(x);update(t);
    if((t->p=y)){
      if(y->l==x) y->l=t;
      if(y->r==x) y->r=t;
      update(y);
    }
  }

  void splay(Node *t){
    eval(t);
    while(!t->is_root()){
      Node *q=t->p;
      if(q->is_root()){
	eval(q);eval(t);
	if(q->l==t) rotR(t);
	else rotL(t);
      }else{
	auto *r=q->p;
	eval(r);eval(q);eval(t);
	if(r->l==q){
	  if(q->l==t) rotR(q),rotR(t);
	  else rotL(t),rotR(t);
	}else{	
	  if(q->r==t) rotL(q),rotL(t);
	  else rotR(t),rotL(t);
	}
      }
    }
  }

  Node* expose(Node *t){
    Node *rp=nullptr;
    for(Node *c=t;c;c=c->p){
      splay(c);
      c->r=rp;
      update(c);
      rp=c;
    }
    splay(t);
    return rp;
  }

  void link(Node *par,Node *c){
    expose(c);
    expose(par);
    c->p=par;
    par->r=c;
  }

  void cut(Node *c){
    expose(c);
    Node *par=c->l;
    c->l=nullptr;
    par->p=nullptr;
  }

  void evert(Node *t){
    expose(t);
    toggle(t);
    eval(t);
  }

  Node *lca(Node *a,Node *b){
    expose(a);
    return expose(b);
  }

  void set_propagate(Node *t,E v){
    expose(t);
    propagate(t,v);
    eval(t);
  }
};

signed GRL_5_C(){
  int n;
  cin>>n;
  using LCT = LinkCutTree<int,int>;
  LCT::F f=[](int a,int b){return min(a,b);};
  LCT::P p=[](int a,size_t b){b++;return a;};
  LCT lc(f,f,f,p,0,0);

  vector<LCT::Node*> v(n);
  for(int i=0;i<n;i++) v[i]=lc.create(i,0);
  for(int i=0;i<n;i++){
    int k;
    cin>>k;
    for(int j=0;j<k;j++){
      int c;
      cin>>c;
      lc.link(v[i],v[c]);
    }
  }
  
  int q;
  cin>>q;
  for(int i=0;i<q;i++){
    int a,b;
    cin>>a>>b;
    cout<<lc.lca(v[a],v[b])->idx<<endl;
  }
  
  return 0;
}

//INSERT ABOVE HERE
signed main(){
  int n,q;
  scanf("%d %d",&n,&q);

  using T = tuple<int,int,int,int,int,int,int>;
  using P = pair<int,int>;
  using LCT = LinkCutTree<T, P>;

  vector<set<int> > G(n); 
  T d1(-1,-1,-1,-1,-1,-1,-1);
  P d0(-1,-114514);
  
  auto con=[&](int a,int b){return G[a].count(b);};
  
  auto f=[&](T a,T b){
    if(a>b) swap(a,b);
    
    if(get<0>(a)<0) return b;
    if(con(get<0>(a),get<1>(b))) swap(a,b);
   
    int al,ar,as,ava,avi,avl,avr;
    tie(al,ar,as,ava,avi,avl,avr)=a;
    int bl,br,bs,bva,bvi,bvl,bvr;
    tie(bl,br,bs,bva,bvi,bvl,bvr)=b;
    
    if(!con(ar,bl)){
      if(con(ar,br)){
	swap(bl,br);
	swap(bvl,bvr);
      }else if(con(al,bl)){
	swap(al,ar);
	swap(avl,avr);
      }else{
	return d1;
      }
    }
    int cl=al,cr=br,cs=as+bs;
    int cva=ava+bva,cvi=max(avi,bvi),cvl=avl,cvr=bvr;
    cvi=max(cvi,avr+bvl);
    cvl=max(cvl,ava+bvl);
    cvr=max(cvr,avr+bva);
    
    return T(cl,cr,cs,cva,cvi,cvl,cvr);
  };
  
  auto g=[&](T a,P p){
    if(p==d0) return a;
    int al,ar,as,ava,avi,avl,avr;
    tie(al,ar,as,ava,avi,avl,avr)=a;
    int v=p.first,b=p.second;
    if(~v) al=ar=v,as=1;
    if(b>=0) return T(al,ar,as,b*as,b*as,b*as,b*as);
    return T(al,ar,as,b*as,b,b,b);
  };
  
  auto h=[&](P a,P b){a.first++;return b;};
  auto p=[&](P a,size_t b){b++;return a;};
  LCT lct(f,g,h,p,d1,d0);
  
  
  vector<int> w(n);
  for(int i=0;i<n;i++) scanf("%d",&w[i]);
  vector<LCT::Node* > vs(n);
  for(int i=0;i<n;i++) vs[i]=lct.create(i,g(d1,P(i,w[i])));
  
  for(int i=0;i<n-1;i++){
    int a,b;
    scanf("%d %d",&a,&b);
    a--;b--;
    G[a].emplace(b);
    G[b].emplace(a);
  }

  if(n==100000) return 0;
  {
    function<void(int,int)> dfs=
      [&](int v,int p){
	if(~p) lct.link(vs[p],vs[v]);
	for(int u:G[v]){
	  if(u==p) continue;
	  dfs(u,v);
	}
      };
    dfs(0,-1);
  }
  if(n==100000) return 0;
  
  while(q--){
    int t,a,b,c;
    scanf("%d %d %d %d",&t,&a,&b,&c);
    a--;b--;
    if(t==1){
      lct.evert(vs[a]);
      lct.set_propagate(vs[b],P(-1,c));      
    }
    if(t==2){
      lct.evert(vs[a]);
      lct.expose(vs[b]);
      int vva,vvi,vvl,vvr;
      tie(ignore,ignore,ignore,vva,vvi,vvl,vvr)=vs[b]->dat;
      printf("%d\n",max({vva,vvi,vvl,vvr}));
    }
  }
  
  return 0;
}