区间最值

https://www.luogu.com.cn/problem/P3865

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
#define lson l,m,st<<1
#define rson m+1,r,st<<1|1
typedef long long ll;
const int maxn = 1e5 + 5;

int a[maxn];
int tree[maxn<<2];

void build(int l,int r,int st)
{
    if(l==r) 
    tree[st]=a[l];
    else
    {
        int m=(l+r)>>1;
        build(lson);
        build(rson);
        tree[st]=max(tree[lson],tree[rson]);
    }
}

int query(int L,int R,int l,int r,int st)
{
    if(L<=l&&r<=R)
    return tree[st];
    int m=(l+r)>>1;
    int ans=0;
    if(L<=m)  ans= max(query(L,R,lson),ans);
    if(m<R)   ans= max(query(L,R,rson),ans);
    return ans;
}


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