区间最大数

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define maxn 100010

struct N
{
int l, r, max;
} tree[maxn * 3]; //注意乘三

int num[maxn];

void build(int node, int l, int r)
{
tree[node].l = l;
tree[node].r = r;

if(l == r)
{
scanf("%d", &tree[node].max);
return ;
}

int mid = (l + r) / 2;
build(node * 2, l, mid);
build(node * 2 + 1, mid + 1, r);
tree[node].max = max(tree[node << 1].max, tree[node << 1 | 1].max);
return ;
}

int query(int node, int ql, int qr)
{
int l = tree[node].l;
int r = tree[node].r;

if(l == ql && r == qr)
return tree[node].max;
//if (l == r) return tree[node].max;
int mid = (l + r) / 2;
if(qr <= mid)
return query(node << 1, ql, qr);
else if(ql > mid)
return query(node << 1 | 1, ql, qr);
else
return max(query(node << 1, ql, mid), query(node << 1 | 1, mid + 1, qr));
}

int main()
{
int n, m;
int ql, qr;
scanf("%d %d", &n, &m);
build(1, 1, n);
for(int i = 0; i < m; i++)
{
scanf("%d %d", &ql, &qr);
printf("%d ", query(1, ql, qr));
}
}