Segment tree (interval addition section cover +)

#include<iostream>
#include<cstdio>
#include<cctype>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<ctime>
#define ls (o<<1)
#define rs (o<<1|1)
using namespace std;
const int N =1e6+5;
inline int read(){
    char x =getchar();  int a =0;
    while(!isdigit(x))  x =getchar();
    while(isdigit(x))   a =a*10+x-48,x =getchar();
    return a;
} 
int val[N<<2],add[N<<2],set[N<<2],n;
inline void update(int o){
    val[o] =max(val[ls],val[rs]);
}
inline void down(int o){
    if(set[o]!=-1){
        val[ls] = val[rs] =set[o];
        set[ls] = set[rs] =set[o];
        add[ls] = add[rs] =0;
        set[o]  =-1;
    }
    else if(add[o]){
        val[ls] +=add[o];
        val[rs] +=add[o];
        if(set[ls]==-1){
            add[ls] +=add[o];
        }
        else{
            set[ls] +=add[o];
        }
        if(set[rs]==-1){
            add[rs] +=add[o];
        }
        else{
            set[rs] +=add[o];
        }
        add[o] =0;
    }
}
inline void modify_set(int o,int l,int r,int ql,int qr,int v){
    if(ql<=l&&r<=qr){
        val[o] =v;
        set[o] =v;
        add[o] =v;
        return ;
    }
    int mid =(l+r) >>1;
    down(o);
    if(ql<=mid){
        modify_set(ls,l,mid,ql,qr,v);
    }
    if(mid+1<=qr){
        modify_set(rs,mid+1,r,ql,qr,v);
    }
    update(o);
}
inline void modify_add(int o,int l,int r,int ql,int qr,int v){
    if(ql<=l&&r<=qr){
        val[o] +=v;
        if(set[o]==-1){
            add[o] +=v;
        }
        else{
            set[o] +=v;
        }
        return ;
    }
    int mid =(l+r) >>1;
    down(o);
    if(ql<=mid){
        modify_add(ls,l,mid,ql,qr,v);
    }
    if(mid+1<=qr){
        modify_add(rs,mid+1,r,ql,qr,v);
    }
    update(o);
}
inline int query(int o,int l,int r,int ql,int qr){
    if(ql<=l&&r<=qr){
        return val[o];
    }
    int mid =(l+r) >>1,ans =0;
    down(o);
    if(ql<=mid){
        ans =max(ans,query(ls,l,mid,ql,qr));
    }
    if(mid+1<=qr){
        ans =max(ans,query(rs,mid+1,r,ql,qr));
    }
    return ans;
}
int main(){
    memset(set,-1,sizeof(set));
    n =read();
    int T =read();
    while(T--){
        int op =read(),x =read(),y =read(),z;
        if(op==1){
            printf("%d\n",query(1,1,n,x,y));
        }
        else if(op==2){
            modify_set(1,1,n,x,y,0);
        }
        else{
            z =read(),modify_add(1,1,n,x,y,z);
        }
    }
}