[AcWing 4340] 我讨厌它

单点修改（更新），区间查询（最大值）

线段树

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点击查看代码

#include<bits/stdc++.h>

using namespace std;

typedef long long LL;

const int N = 5e5 + 10;

int n, m;
int w[N];

struct Node
{
    int l, r;
    int v;
} tr[N * 4];

void pushup(int u)
{
    tr[u].v = max(tr[u << 1].v, tr[u << 1 | 1].v);
}

void bulid(int u, int l, int r)
{
    if (l == r)
        tr[u] = {l, r, w[l]};
    else {
        tr[u] = {l, r, 0};
        int mid = l + r >> 1;
        bulid(u << 1, l, mid);
        bulid(u << 1 | 1, mid + 1, r);
        pushup(u);
    }
}

void modify(int u, int x, int v)
{
    if (tr[u].l == tr[u].r)
        tr[u].v = v;
    else {
        int mid = tr[u].l + tr[u].r >> 1;
        if (x <= mid)
            modify(u << 1, x, v);
        else
            modify(u << 1 | 1, x, v);
        pushup(u);
    }
}

int query(int u, int l, int r)
{
    if (tr[u].l >= l && tr[u].r <= r)
        return tr[u].v;
    else {
        int mid = tr[u].l + tr[u].r >> 1;
        int res = 0;
        if (l <= mid)
            res = max(res, query(u << 1, l, r));
        if (r > mid)
            res = max(res, query(u << 1 | 1, l, r));
        return res;
    }
}

void solve()
{
    while (cin >> n >> m) {
        for (int i = 1; i <= n; i ++)
        cin >> w[i];
        bulid(1, 1, n);
        while (m --) {
            char op;
            int l, r;
            cin >> op >> l >> r;
            if (op == 'U')
                modify(1, l, r);
            else
                cout << query(1, l, r) << endl;
        }
    }
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    solve();

    return 0;
}

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1. 只需要维护区间最大值即可