P1531 I Hate It 树状数组解法

P1531 I Hate It
区间最大值，区间查询最大值，单点更新，本解使用树状数组求解

#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
 
const int MAXN = 3e5;
int a[MAXN], h[MAXN];
int n, m;
 
int lowbit(int x)
{
	return x & (-x);
}
void updata(int x)
{
	int lx, i;
	while (x <= n)
	{
		h[x] = a[x];
		lx = lowbit(x);
		for (i=1; i<lx; i<<=1)
			h[x] = max(h[x], h[x-i]);
		x += lowbit(x);
	}		
}
int query(int x, int y)
{
	int ans = 0;
	while (y >= x)
	{
		ans = max(a[y], ans);
		y --;
		for (; y-lowbit(y) >= x; y -= lowbit(y))
			ans = max(h[y], ans);
	}
	return ans;
}
int main()
{
	int i, j, x, y, ans;
	char c[10];
	scanf("%d %d",&n,&m); 
	for (i=1; i<=n; i++)
		h[i] = 0;
	for (i=1; i<=n; i++)
	{
		scanf("%d",&a[i]);
		updata(i);
	}
	for (i=1; i<=m; i++)
	{
		cin>>c;
		if (c[0]== 'Q')
		{
			scanf("%d %d",&x,&y);
			ans = query(x, y);
			printf("%d\n",ans);
		}
		else if (c[0] == 'U')
		{
			scanf("%d %d",&x,&y);
			if (a[x]<y)
			{
				a[x] = y;
				updata(x);
			}
			
		}
	}
	return 0;
}