LC#509 finds nth fibonacci number, recursive & DP approach

Author: NirmalSilwal

Leetcode/leetcodeTags/array/FibonacciNumber509.java

@@ -0,0 +1,54 @@
+package leetcodeTags.array;
+
+import java.util.Arrays;
+
+public class FibonacciNumber509 {
+
+	// using recursion
+	public static int fib(int n) {
+		if (n == 0 || n == 1)
+			return n;
+
+		int fibonacci = fib(n - 1) + fib(n - 2);
+		return fibonacci;
+	}
+
+	// using DP
+	public static int fibDP(int n) {
+		if (n == 0 || n == 1)
+			return n;
+
+		int[] storage = new int[n + 1];
+		Arrays.fill(storage, -1); // initializing DP array with -1
+
+		// filling first two positions
+		storage[0] = 0;
+		storage[1] = 1;
+		
+		return fibTopDown(n, storage);
+	}
+
+	private static int fibTopDown(int n, int[] storage) {
+		if (n == 0 || n == 1)
+			return n;
+
+		if (storage[n] != -1)
+			return storage[n];
+
+		int fibonacci = fibTopDown(n - 1, storage) + fibTopDown(n - 2, storage);
+		storage[n] = fibonacci;
+
+		return fibonacci;
+	}
+
+	public static void main(String[] args) {
+		for (int i = 0; i <= 7; i++) {
+			System.out.println(fib(i));
+		}
+
+		System.out.println("\ntesting DP code\n");
+		for (int i = 0; i <= 7; i++) {
+			System.out.println(fibDP(i));
+		}
+	}
+}