洛谷 P3865 【模板】ST表

题目链接

https://www.luogu.org/problem/P3865

分析

ST表使用倍增思想，一般用于解决 $O(nlogn)$ 预处理，$O(1)$ 查询的静态区间最值问题。

AC代码

#include 
#include 

using namespace std;

inline int read() {
	int num = 0;
	char c = getchar();
	while (c < '0' || c > '9') c = getchar();
	while (c >= '0' && c <= '9')
		num = num * 10 + c - '0', c = getchar();
	return num;
}

const int maxn = 1e5 + 5;

int f[maxn][20], k[maxn];

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