I hate it （线段树）

5 6
1 2 3 4 5
Q 1 5
U 3 6
Q 3 4
Q 4 5
U 2 9
Q 1 5 

5
6
5
9 

Huge input,the C function scanf() will work better than cin 

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
#define maxn 200005
#define inf 0x3f3f3f3f
int sum[maxn<<2],ll[maxn<<2],rr[maxn<<2];
int a[maxn];
inline void pushup(int i){
    sum[i]=max(sum[i<<1],sum[(i<<1)|1]);
}
void build(int l,int r,int i){
    ll[i]=l;
    rr[i]=r;
    if(l==r){
        sum[i]=a[l];
        return;
    }
    int m=(ll[i]+rr[i])>>1,ls=i<<1,rs=ls|1;
    build(l,m,ls);
    build(m+1,r,rs);
    pushup(i);
}
void update(int k,int v,int i){
    if(ll[i]==rr[i]){
        sum[i]=v;
        return ;
    }
    int m=(ll[i]+rr[i])>>1,ls=i<<1,rs=ls|1;
    if(k<=m)update(k,v,ls);
    else update(k,v,rs);
    pushup(i);
}
int query(int l,int r,int i){
    if(l<=ll[i]&&rr[i]<=r){
        return sum[i];
    }
    int m=(ll[i]+rr[i])>>1,ls=i<<1,rs=ls|1;
    int ans=0;
    if(l<=m)ans=max(query(l,r,ls),ans);
    if(m<r)ans=max(query(l,r,rs),ans);
    return ans;
}
int main()
{
    int n,m;
    int u,v;
    //freopen("in.txt","r",stdin);
    while(~scanf("%d%d",&n,&m)){
        for(int i=1;i<=n;i++){
            scanf("%d",&a[i]);
        }
        build(1,n,1);
        char q[2];
        while(m--){
            scanf("%s %d %d",q,&u,&v);       //用c会出问题
            if(q[0]==‘Q‘){
                printf("%d\n",query(u,v,1));
            }
            else {
                update(u,v,1);
            }
        }
    }
}