HDU 1754 I Hate it

#include <iostream>
#define MAXSIZE 200001
using namespace std;

struct node
{
    int l,r;
    int max;
}tree[MAXSIZE*4];

int num[MAXSIZE];

void build(int root,int l,int r)
{
    tree[root].l = l;
    tree[root].r = r;
    
    if(l == r)
    {
        tree[root].max = num[l];
        return;
    }
    
    int mid = (r+l)/2;
    
    build(root*2,l,mid);
    build(root*2+1,mid+1,r);
    tree[root].max = max(tree[root*2].max,tree[root*2+1].max);
}

void update(int root,int pos,int value)
{
    if(tree[root].r == pos&&tree[root].l == pos)
    {
        tree[root].max = value;
        return;
    } 
    
    int mid = (tree[root].r+tree[root].l)/2;
    
    if(pos<=mid)
        update(root*2,pos,value);
    else
    {
        update(root*2+1,pos,value);
    } 
    
    tree[root].max = max(tree[root*2].max,tree[root*2+1].max); 
}

int query(int root,int l,int r)
{
    if(r>=tree[root].r&&l<=tree[root].l)
        return tree[root].max;
    
    
    int mid = (tree[root].r+tree[root].l)/2;
    
    if(l>mid)
        return query(root*2+1,l,r);
    else if(r<=mid)
        return query(root*2,l,r);
    else
    {
        int a = query(root*2,l,mid);
        int b = query(root*2+1,mid+1,r);
        return max(a,b);
    }
}

int main()
{
    int n,m;
    char t;
    int a,b;
    while(scanf("%d %d",&n,&m)!=EOF)
    {
        getchar();
        for(int i = 1;i<=n;i++)
        {
            scanf("%d",num+i);
            getchar();
        }
        
        build(1,1,n);
        
        for(int i=0;i<m;i++)
        {
            scanf("%c %d %d",&t,&a,&b);
            getchar();
            if(t==‘Q‘)
            {
                cout<<query(1,a,b)<<endl;
            }
            else
                update(1,a,b);
        }
    }
    return 0;
}