luoguP1253 扶苏的问题

给定长度为n的序列A，有如下3种操作：

• 1 l r x，将区间[l,r]中的每个数都修改为x。
• 2 l r x，将区间[l,r]中的每个数都加上x。
• 3 l r，查询区间[l,r]内的最大值。

分析：设置2个懒标记，先处理赋值标记，再处理增加标记。

#include <bits/stdc++.h>
using llong = long long;

const llong inf = 1e18;

// LazySegmentTree模板...

struct Tag {
    llong set;
    llong add;
    Tag(llong s=inf, llong a=inf):set(s),add(a) {}
    void apply(Tag t) {
        if (t.set != inf) {
            set = t.set;
            add = inf;
        }
        if (t.add != inf) {
            if (add == inf) {
                add = t.add;
            } else {
                add += t.add;
            }
        }
    }
    friend std::ostream& operator<<(std::ostream &out, Tag &tag) {
        out << "tag:(" << tag.set << "," << tag.add << ")";
        return out;
    }
};

struct Info {
    llong max;
    Info(llong a=-inf):max(a) {}
    void apply(Tag t) {
        if (t.set != inf) {
            max = t.set;
        }
        if (t.add != inf) {
            max += t.add;
        }
    }
    friend Info operator+(const Info &a, const Info &b) {
        Info ans;
        ans.max = std::max(a.max, b.max);
        return ans;
    }
    friend std::ostream& operator<<(std::ostream &out, Info &info) {
        out << "info:(" << info.max << ")";
        return out;
    }
};

void solve() {
    int n, m;
    std::cin >> n >> m;
    std::vector<llong> A(n);
    for (int i = 0; i < n; i++) {
        std::cin >> A[i];
    }
    LazySegmentTree<Info,Tag> tr(A);
    for (int i = 0; i < m; i++) {
        int op, l, r, x;
        std::cin >> op >> l >> r;
        if (op == 1) {
            std::cin >> x;
            tr.rangeApply(l-1, r, Tag(x, inf));
        } else if (op == 2) {
            std::cin >> x;
            tr.rangeApply(l-1, r, Tag(inf, x));
        } else if (op == 3) {
            std::cout << tr.rangeQuery(l-1, r).max << "\n";
        }
    }
}

int main() {
    std::cin.tie(0)->sync_with_stdio(0);
    int t = 1;
    while (t--) solve();
    return 0;
}