hdu 1754 线段树模板题

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1754

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <vector>

#define maxn 230050
#define lson l,mid,u<<1
#define rson mid+1,r,u<<1|1
using namespace std;

const int INF = 0x3f3f3f;

int seg[maxn<<2];

int Push_UP(int u){
    seg[u] = max(seg[u<<1],seg[u<<1|1]);  //****这个地方 u<<1|1 不能换为 u << 1 +1 
}
void build(int l,int r,int u){
    if(l == r){
        scanf("%d",&seg[u]);
        return;
    }
    int mid = (l + r)/2; 
    build(lson);
    build(rson);
    Push_UP(u);
}
void Update(int loc,int num,int l,int r,int u){
    if(l == r){  // 这个地方要注意！！ 
        seg[u] = num;  
        return;
    }
    int mid = (l + r)/2; 
    if(loc <= mid) Update(loc,num,lson);
    else           Update(loc,num,rson);
    Push_UP(u);
}
int Query(int L,int R,int l,int r,int u){
    if(L <= l && r <= R){
        return seg[u];
    }
    int ret = 0;  
    int mid = (l + r)/2;
    if(L <= mid)    ret =max(ret,Query(L,R,lson));
    if(R >  mid)    ret =max(ret,Query(L,R,rson));
    return ret;
}
int main()
{
    if(freopen("input.txt","r",stdin)== NULL)  {printf("Error
"); exit(0);}
    int N,M;
    while(cin>>N>>M){
        build(1,N,1); 
        while(M--){
            char query[2];
            int l,r;
            scanf("%s%d%d",query,&l,&r);
            if(query[0] == 'U')  Update(l,r,1,N,1);
            else{ 
                int ans = Query(l,r,1,N,1);
                printf("%d
",ans);
            }
        }
    }
}