ST表模板

#include <iostream>

using namespace std;


// f[i, j] = [i, 2^j-1] 的最大值    即：  从i开始， 连续 2^j 个数的最大值。

const int N = 1e5 + 5;

int arr[N];

int ST[N][18];
int log2[N] = {-1};
 
int read()
{
	int x = 0, f = 1;
	char c = getchar();
	while(c < '0' || c > '9') 
	{
		if(c == '-') f = 1; c = getchar();
	}
	while(c >= '0' && c <= '9')
	{
		x = x * 10 + c - 48;
		c = getchar();
	}
	return x*f;
}

int main()
{
	int n = read(), m = read();
	for(int i = 1; i <= n; i++)
	{
		arr[i] = read();
		log2[i] = log2[i/2] + 1;
		ST[i][0] = arr[i];
	}
	
	for(int j = 1; j <= log2[n]; j++)
	{
		for(int i = 1; i + (1<<j)-1 <= n; i++)
		{
			ST[i][j] = max(ST[i][j-1], ST[i+(1<<(j-1))][j-1]);
		}
	}	
	
	int l, r, k;
	for(int i = 0; i < m; i++)
	{
		l = read();
		r = read();
		k = log2[r-l+1];
		printf("%d\n", max(ST[l][k], ST[r - (1<<k)+1][k]));
	}
	
	return 0;
}