hdu 1754 线段树（单点替换 区间最值）

Sample Input
5 6
1 2 3 4 5
Q 1 5 //1-5结点的最大值
U 3 6 //将点3的数值换成6
Q 3 4
Q 4 5
U 2 9
Q 1 5

Sample Output
5
6
5
9

 # include <iostream>
 # include <cstdio>
 # include <cstring>
 # include <algorithm>
 # include <cmath>
 # include <queue>
 # define LL long long
 using namespace std ;

 const int maxn = ;

 int MAX[maxn<<] ; //结点开4倍

 void PushUP(int rt) //更新到父节点
 {
     MAX[rt] = max(MAX[rt * ] , MAX[rt *  + ] ); //rt 为当前结点
 }

 void build(int l , int r , int rt) //构建线段树
 {
     if (l == r)
     {
         scanf("%d" , &MAX[rt]) ;
         return ;
     }
     int m = (l + r) /  ;
     build(l , m , rt * ) ;
     build(m +  , r , rt *  +) ;
     PushUP(rt) ;
 }

 void updata(int p , int add , int l , int r , int rt)  //单点替换
 {
     if (l == r)
     {
         MAX[rt] = add ;
         return ;
     }
     int m = (l + r) /  ;
     if (p <= m)
        updata(p , add , l , m , rt * ) ;
     else
        updata(p , add , m +  , r , rt *  + ) ;
     PushUP(rt) ;
 }

 int query(int L , int R , int l , int r , int rt)  //区间求最大值
 {
     if (L <= l && r <= R)
         return MAX[rt] ;
     int m = (l + r) /  ;
     int ret =  ;
     if (L <= m)
        ret = max(ret , query(L , R , l , m , rt * ) ) ;
     if (R > m)
        ret = max(ret , query(L , R , m +  , r , rt *  + ) );
     return ret ;
 }

 int main ()
 {
     //freopen("in.txt","r",stdin) ;
     int n , m ;
     while(scanf("%d %d" , &n , &m) != EOF)
     {
         build( , n , ) ;
         char op[] ;
         while(m--)
         {
             scanf("%s" , op) ;
             if (op[] == 'E') //结束
                break ;
             int a , b ;
             scanf("%d %d" , &a , &b) ;
             if (op[] == 'Q') //求a,b区间的和最大值
                printf("%d\n", query(a , b ,  , n , ))  ;
             else if (op[] == 'U')  //将第a个地方的值改为b
                updata(a , b ,  , n , ) ;
         }
     }

     return  ;
 }