LC#70 finds no. of ways to climb stairs of N steps, recursive & DP solution

Author: NirmalSilwal

Leetcode/easy/ClimbingStairs70.java

@@ -0,0 +1,58 @@
+package easy;
+
+import java.util.Arrays;
+
+public class ClimbingStairs70 {
+
+	// this gives TLE for n >= 42
+	public static int climbStairs(int n) {
+
+		if (n == 0)
+			return 1;
+
+		if (n < 0)
+			return 0;
+
+		int oneStep = climbStairs(n - 1);
+		int twoStep = climbStairs(n - 2);
+
+		int totalClimbPossible = oneStep + twoStep;
+
+		return totalClimbPossible;
+	}
+
+	// optimal code
+	public static int climbStairsDP(int n, int[] storage) {
+
+		if (n == 0)
+			return 1;
+
+		if (n < 0)
+			return 0;
+
+		if (storage[n] != -1)
+			return storage[n];
+
+		int oneStep = climbStairsDP(n - 1, storage);
+		int twoStep = climbStairsDP(n - 2, storage);
+
+		int totalClimbPossible = oneStep + twoStep;
+
+		storage[n] = totalClimbPossible;
+
+		return totalClimbPossible;
+	}
+
+	public static void main(String[] args) {
+
+		// using Recrusive approach only
+		int n = 45;
+
+		// System.out.println(climbStairs(n));
+
+		// using DP
+		int[] storage = new int[n + 1];
+		Arrays.fill(storage, -1);
+		System.out.println(climbStairsDP(n, storage));
+	}
+}