P1531 I Hate It

P1531 I Hate It

树状数组求区间最大值

#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N=2e5+10;
int n,m;
int tr[N*4],a[N];
int lowbit(int x){
	return x&-x;
}
void change(int x,int y){
	for(int i=x;i<=n;i+=lowbit(i))	tr[i]=max(tr[i],y);
}
int query(int x,int i){
	int res=0;
	for(;i-lowbit(i)>=x;i-=lowbit(i))	res=max(res,tr[i]);
	for(;i>=x;i--)	res=max(res,a[i]);
	return res;
}
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		change(i,a[i]);
	}
	while(m--){
		char c;
		int x,y;
		cin>>c;
		if(c=='U'){
			cin>>x>>y;
			change(x,y);
			a[x]=max(a[x],y);
		}else{
			cin>>x>>y;
			cout<<query(x,y)<<endl;
		}
	}
	return 0;
}