HDU 1754 线段树

#include <stdio.h>
typedef struct NODE {
    int lc,rc;
    int grade;
    int first,mid,tail;
}node;

node s[600005];
int gra[200005];

int Max(int a,int b){return a>b?a:b;}

void Maketree(int first,int tail,int at){
    s[at].first = first;
    s[at].tail = tail;
    if( first == tail )
        s[at].grade = gra[first];
    else{
        s[at].lc = at*2;
        s[at].rc = at*2+1;
        s[at].mid = (first+tail) / 2;
        Maketree(first,s[at].mid,s[at].lc);
        Maketree(s[at].mid+1,tail,s[at].rc);
        s[at].grade = Max( s[s[at].lc].grade , s[s[at].rc].grade);
    }
}
int Query(int first,int tail,int at){
    int l,r;
    if( s[at].first == first && s[at].tail == tail )
        return s[at].grade;
    if( first > s[at].mid ) return Query(first,tail,s[at].rc);
    else if( tail < s[at].mid+1 ) return Query(first,tail,s[at].lc);
    else{
        l = Query(first , s[at].mid , s[at].lc);
        r = Query(s[at].mid+1 , tail , s[at].rc);
        return l > r ? l : r ;
    }
}
void Updata(int i,int grade,int at){
    if( s[at].first == s[at].tail ){
        s[at].grade = grade;
    }
    else{
        if( i <= s[at].mid ){
            Updata(i,grade,s[at].lc);
        }
        else Updata(i,grade,s[at].rc);
        s[at].grade = Max( s[s[at].lc].grade , s[s[at].rc].grade );
    }
}

int main(){
    int n,m,i,a,b;
    char c;
    while(scanf("%d%d",&n,&m)!=EOF){
        for( i = 1 ; i <= n ; i++){
            scanf("%d",&gra[i]);
        }
        Maketree(1,n,1);
        while(m--){

getchar();
            scanf("%c%d%d",&c,&a,&b);
            if( c == 'Q' ) printf("%d\n",Query(a,b,1));
            if( c == 'U' ) Updata(a,b,1);
        }
    }
    return 0;
}