代码：

#include<bits/stdc++.h>
#define int long long

using namespace std;

const int N = 1e6 + 5;
const int inf = 1e18;

int n, m;
int a[N];

int tree[N * 4], tag1[N * 4], tag2[N * 4];

void pushup(int node){
  tree[node] = max(tree[node << 1], tree[node << 1 | 1]);
}

void addtag1(int node, int lt, int rt, int val){    //赋值
  tag1[node] = val;
  tag2[node] = 0;
  tree[node] = val;
}

void addtag2(int node, int lt, int rt, int val){
  tag2[node] += val;
  tree[node] += (rt - lt + 1) * val;
}

void pushdown(int node, int lt, int rt){
  // if(!tag1[node] && !tag2[node]){
  //   return ;
  // }
  int mid = lt + rt >> 1;
  if(tag1[node] != inf){
    addtag1(node << 1, lt, mid, tag1[node]);
    addtag1(node << 1 | 1, mid + 1, rt, tag1[node]);
    tag1[node] = inf;
  }
  if(tag2[node]){
    addtag2(node << 1, lt, mid, tag2[node]);
    addtag2(node << 1 | 1, mid + 1, rt, tag2[node]);
    tag2[node] = 0;
  }
}

void build(int node, int lt, int rt){
  if(lt == rt){
    tree[node] = a[lt];
    return ;
  }
  int mid = lt + rt >> 1;
  build(node << 1, lt, mid);
  build(node << 1 | 1, mid + 1, rt);
  pushup(node);
}

void update1(int node, int lt, int rt, int x, int y, int val){     //赋值
  if(x > rt || y < lt){
    return ;
  }
  if(x <= lt && rt <= y){
    addtag1(node, lt, rt, val);
    return ;
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  update1(node << 1, lt, mid, x, y, val);
  update1(node << 1 | 1, mid + 1, rt, x, y, val);
  pushup(node);
}

void update2(int node, int lt, int rt, int x, int y, int val){     //赋值
  if(x > rt || y < lt){
    return ;
  }
  if(x <= lt && rt <= y){
    addtag2(node, lt, rt, val);
    return ;
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  update2(node << 1, lt, mid, x, y, val);
  update2(node << 1 | 1, mid + 1, rt, x, y, val);
  pushup(node);
}

int query(int node, int lt, int rt, int x, int y){     //赋值
  if(x > rt || y < lt){
    return -1e18;
  }
  if(x <= lt && rt <= y){
    return tree[node];
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  return max(query(node << 1, lt, mid, x, y), query(node << 1 | 1, mid + 1, rt, x, y));
}

void Solve(){
  cin >> n >> m;
  for(int i = 1; i <= n; i++){
    cin >> a[i];
  }
  build(1, 1, n);
  for(int i = 1; i <= 4 * n; i++){
    tag1[i] = inf;
  }
  while(m--){
    int op;
    cin >> op;
    if(op == 1){
      int x, y, k;
      cin >> x >> y >> k;
      update1(1, 1, n, x, y, k);
    }
    else if(op == 2){
      int x, y, k;
      cin >> x >> y >> k;
      update2(1, 1, n, x, y, k);
    }
    else{
      int x, y;
      cin >> x >> y;
      cout << query(1, 1, n, x, y) << '\n';
    }
  }
}

signed main(){
  Solve();
  return 0;
}

更奇妙的是，最后一个点开 O2 都 T 了。