50pts，有 WA 有 TLE ： https://www.luogu.com.cn/record/67962422

自己拍了一下小数据范围，拍了 1000 组没问题。洛谷上给的下载数据没有调试意义，所以恳求大佬们帮忙看看我的代码或提供一下 hack 数据。

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

#define int long long
#define maxn 1000005
struct SegmentTree {
    int l, r;
    int dat, add = 0, flag = -maxn;
} t[maxn * 4];
int n, m;
int a[maxn];

void build(int p, int l, int r) {
    t[p].l = l, t[p].r = r;
    if (l == r) { t[p].dat = a[l]; return; }
    int mid = (l + r) >> 1;
    build(p << 1, l, mid), build((p << 1) | 1, mid + 1, r);
    t[p].dat = max(t[p << 1].dat, t[(p << 1) | 1].dat);
}

void spread(int p) {
    if (t[p].flag != -maxn) {
        t[p << 1].dat = t[p].flag, t[(p << 1) | 1].dat = t[p].flag;
        t[p << 1].flag = t[(p << 1) | 1].flag = t[p].flag;
        t[p].flag = -maxn;
    }
    if (t[p].add) {
        t[p << 1].dat += t[p].add, t[(p << 1) | 1].dat += t[p].add;
        t[p << 1].add += t[p].add, t[(p << 1) | 1].add += t[p].add;
        t[p].add = 0;
    }
}

void change1(int p, int l, int r, int k) {
    if (l <= t[p].l && r >= t[p].r) {
        t[p].dat = k;
        t[p].add = 0, t[p].flag = k;
        return;
    }
    spread(p);
    int mid = (t[p].l + t[p].r) >> 1;
    if (l <= mid) change1(p << 1, l, r, k);
    if (r > mid) change1((p << 1) | 1, l, r, k);
    t[p].dat = max(t[p << 1].dat, t[(p << 1) | 1].dat);
}

void change2(int p, int l, int r, int k) {
    if (l <= t[p].l && r >= t[p].r) {
        t[p].dat += k;
        t[p].add += k;
        return;
    }
    spread(p);
    int mid = (t[p].l + t[p].r) >> 1;
    if (l <= mid) change2(p << 1, l, r, k);
    if (r > mid) change2((p << 1) | 1, l, r, k);
    t[p].dat = max(t[p << 1].dat, t[(p << 1) | 1].dat);
}

int ask(int p, int l, int r) {
    if (l <= t[p].l && r >= t[p].r) return t[p].dat;
    spread(p);
    int mid = (t[p].l + t[p].r) >> 1, val = -maxn;
    if (l <= mid) val = max(val, ask(p << 1, l, r));
    if (r > mid) val = max(val, ask((p << 1) | 1, l, r));
    return val;
}

signed main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) cin >> a[i];
    build(1, 1, n);
    for (int i = 1; i <= m; i++) {
        int op, l, r, x;
        cin >> op >> l >> r;
        if (op == 1) { cin >> x; change1(1, l, r, x); }
        else if (op == 2) { cin >> x; change2(1, l, r, x); }
        else cout << ask(1, l, r) << endl;
    }
    return 0;
}