hdu_1754，线段树单点更新，求区间最值

http://www.notonlysuccess.com/index.php/segment-tree-complete/

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define maxn 2222222
using namespace std;
int a[maxn<<2];
void pushUp(int rt)
{
    a[rt]=max(a[rt<<1],a[rt<<1|1]);
}
void build(int l,int r,int rt)
{
    if(l==r)
    {
        scanf("%d",&a[rt]);
        return ;
    }
    int m=(r+l)>>1;
    build(lson);
    build(rson);
    pushUp(rt);
}
void update(int p,int sc,int l,int r,int rt)
{
    if(l==r)
    {
        a[rt]=sc;
        return;
    }
    int m=(l+r)>>1;
    if(p<=m) update(p,sc,lson);
    else update(p,sc,rson);
    pushUp(rt);
}
int query(int L,int R,int l,int r,int rt)
{
    int x=0;
    if(L<=l&&r<=R)
        return a[rt];
    int m=(r+l)>>1;
    if(L<=m) x=max(x,query(L,R,lson));
    if(R>m) x=max(x,query(L,R,rson));
    return x;
}
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        build(1,n,1);
        char c[2];
        int d,e;
        for(int i=0; i<m; i++)
        {
            scanf("%s%d%d",c,&d,&e);
            if(c[0]=='Q')
            {
                printf("%d\n",query(d,e,1,n,1));
            }
            if(c[0]=='U')
            {
                update(d,e,1,n,1);
            }
        }
    }
    return 0;
}