由于自己做代码优化时，条件不清晰，两个变量写错导致WA了两次，不应该！
#include<iostream>
#include<cstdio>
#define MAXN 222222
using namespace std;int tree[MAXN<<2];
int N,M;void pushUp( int rt )
{tree[rt]=max(tree[rt<<1],tree[rt<<1|1]);
}void build( int l,int r,int rt )
{if( l==r ){scanf( "%d",&tree[rt] );return ;}int m=(l+r)/2;build( l,m,rt<<1 );build( m+1,r,rt<<1|1 );pushUp(rt);
}int query( int L,int R,int l,int r,int rt )
{if( L<=l&&r<=R )return tree[rt];int m=(l+r)/2,ret=0;if( m>=R )return query( L,R,l,m,rt<<1 );if( m+1<=L )return query( L,R,m+1,r,rt<<1|1 );ret=max(ret,query(L,R,l,m,rt<<1));ret=max(ret,query(L,R,m+1,r,rt<<1|1));return ret;
}void update( int pt,int v,int l,int r,int rt )
{if( l==r ){tree[rt]=v;return ;}int m=(l+r)/2;if( pt<=m )update( pt,v,l,m,rt<<1 );elseupdate( pt,v,m+1,r,rt<<1|1 );pushUp(rt);
}int main()
{while( scanf("%d %d",&N,&M)!=EOF ){build( 1,N,1 );char str[111];gets(str);while( M-- ){gets(str);int n1,n2;if( sscanf(str,"Q %d %d",&n1,&n2) )printf( "%d\n",query(n1,n2,1,N,1) );else if( sscanf(str,"U %d %d",&n1,&n2) )update( n1,n2,1,N,1 );}}return 0;
}