Acwing 1270. 数列区间最大值

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <climits>

using namespace std;

const int N = 100010;

int n, m;
int w[N];
struct Node
{
    int l, r;
    int maxv;
}tr[N * 4];

void build(int u, int l, int r)
{
    if (l == r) tr[u] = {l, r, w[r]};
    else
    {
        tr[u] = {l, r};
        int mid = l + r >> 1;
        build(u << 1, l, mid), build(u << 1 | 1, mid + 1, r);
        tr[u].maxv = max(tr[u << 1].maxv, tr[u << 1 | 1].maxv);
    }
}

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

int main()
{
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= n; ++ i) scanf("%d", &w[i]);
    
    build(1, 1, n);
    
    int l, r;
    while (m --)
    {
        scanf("%d %d", &l, &r);
        printf("%d\n", query(1, l, r));
    }
    
    return 0;
}