ST表求静态区间最大值

Author: Dev-XYS

Sparse-Table.cpp

@@ -0,0 +1,68 @@
+#include <cstdio>
+#include <cmath>
+
+using namespace std;
+
+int n, m;
+int st[1000010][21], pow2[21];
+
+inline int max(int x, int y)
+{
+	return x > y ? x : y;
+}
+
+inline int _log2(int x)
+{
+	int res = 0;
+	while (x > 1)
+	{
+		x >>= 1;
+		res++;
+	}
+	return res;
+}
+
+void init_pow2()
+{
+	pow2[0] = 1;
+	for (int i = 1; i <= 20; i++)
+	{
+		pow2[i] = pow2[i - 1] * 2;
+	}
+}
+
+void build_st()
+{
+	init_pow2();
+	for (int i = 1; i <= 20; i++)
+	{
+		for (int j = 0; j < n; j++)
+		{
+			st[j][i] = max(st[j][i - 1], st[j + pow2[i - 1]][i - 1]);
+		}
+	}
+}
+
+int get_max(int l, int r)
+{
+	int x = _log2(r - l + 1);
+	return max(st[l][x], st[r - pow2[x] + 1][x]);
+}
+
+int main()
+{
+	scanf("%d%d", &n, &m);
+	for (int i = 0; i < n; i++)
+	{
+		scanf("%d", &st[i][0]);
+	}
+	build_st();
+	for (int i = 0; i < m; i++)
+	{
+		int a, b;
+		scanf("%d%d", &a, &b);
+		printf("%d\n", get_max(a - 1, b - 1));
+	}
+	
+	return 0;
+}