线段树 20pts 求调，带注释

#include <bits/stdc++.h>
#define int long long
#define max(x,y) (((x)>(y))?(x):(y))
#define MIN LONG_LONG_MIN
using namespace std;
const int maxn =1e6+3;
int n,q;
int a[maxn],t[4*maxn],tagm[4*maxn],tagp[4*maxn];// m 修改tag p 增加tag
inline void pushup(int p) {
    t[p] = max(t[p<<1],t[p<<1|1]);
}
inline void pushdown(int p,int l,int r) {
    if (tagm[p] != MIN) {
        t[p<<1] = t[p<<1|1] = tagm[p];
        tagm[p<<1] = tagm[p<<1|1] = tagm[p];
        tagp[p<<1] = tagp[p<<1|1] = 0;
    }
    t[p<<1] += tagp[p];
    t[p<<1|1] += tagp[p];
    tagp[p<<1] += tagp[p];
    tagp[p<<1|1] += tagp[p];
    tagm[p] = MIN,tagp[p] = 0;
}
inline void build(int p,int l,int r) {
    if (l == r) {
        t[p] = a[l];
        tagm[p] = MIN;
        return;
    }
    int mid = (l + r) >> 1;
    build(p<<1,l,mid);
    build(p<<1|1,mid+1,r);
    pushup(p);
}
inline void modifym(int p,int l,int r,int x,int s,int e) {
    if (l <= s && e <= r) {
        t[p] = x;
        tagp[p] = 0;
        tagm[p] = x;
        return;
    }
    int mid = (s + e) >> 1;
    if ((tagp[p] != 0 || tagm[p] != MIN)) pushdown(p,s,e);
    if (l <= mid) modifym(p<<1,l,r,x,s,mid);
    if (r > mid) modifym(p<<1|1,l,r,x,mid+1,e);
    pushup(p);
}//赋值修改
inline void modifyp(int p,int l,int r,int x,int s,int e) {
    if (l <= s && e <= r) {
        t[p] += x;
        tagp[p] += x;
        return;
    }
    int mid = (s + e) >> 1;
    if ((tagp[p] != 0 || tagm[p] != MIN)) pushdown(p,s,e);
    if (l <= mid) modifyp(p<<1,l,r,x,s,mid);
    if (r > mid) modifyp(p<<1|1,l,r,x,mid+1,e);
    pushup(p);
}//增加修改
inline int query(int p,int l,int r,int s,int e) {
    if (l <= s && e <= r) {
        return t[p];
    }
    int mid = (s + e) >> 1;
    if ((tagp[p] != 0 || tagm[p] != MIN)) pushdown(p,s,e);
    int ret = MIN;
    if (l <= mid) ret = max(ret,query(p<<1,l,r,s,mid));
    if (r > mid) ret = max(ret,query(p<<1|1,l,r,mid+1,e));
    return ret;
}
signed main () {
    cin >> n >> q;
    for (int i = 1; i <= n; i++) cin >> a[i];
    build(1,1,n);
    while (q--) {
        int op,l,r;
        cin >> op >> l >> r;
        if (op == 1) {
            int x;
            cin >> x;
            modifym(1,l,r,x,1,n);
        }else if (op == 2) {
            int x;
            cin >> x;
            modifyp(1,l,r,x,1,n);
        }else{
            cout << query(1,l,r,1,n) << '\n';
        }
    }
    return 0;
}