Create Climbing_Stairs

questions/java/Climbing_Stairs

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+// Using Recursion
+
+class stairs { 
+    // A simple recursive program to find 
+    // n'th fibonacci number 
+    static int fib(int n) 
+    { 
+        if (n <= 1) 
+            return n; 
+        return fib(n - 1) + fib(n - 2); 
+    } 
+
+    // Returns number of ways to reach s'th stair 
+    static int countWays(int s) { return fib(s + 1); } 
+
+    /* Driver program to test above function */
+    public static void main(String args[]) 
+    { 
+        int s = 4; 
+        System.out.println("Number of ways = "
+                           + countWays(s)); 
+    } 
+}
+
+//Time Complexity: O(2n)
+//Auxiliary Space: O(n)
+
+// Using Dynamic Programming
+
+
+// Java program to count number of 
+// ways to reach Nth stair 
+class GFG { 
+
+    // A simple recursive function to find number of ways to 
+    // reach the nth stair 
+    static int countWays(int n, int dp[]) 
+    { 
+        if (n <= 1) 
+            return dp[n] = 1; 
+
+        if (dp[n] != -1) { 
+            return dp[n]; 
+        } 
+        dp[n] = countWays(n - 1, dp) + countWays(n - 2, dp); 
+        return dp[n]; 
+    } 
+
+    // Driver code 
+    public static void main(String[] args) 
+    { 
+        int n = 4; 
+        int[] dp = new int[n + 1]; 
+        for (int i = 0; i < n + 1; i++) { 
+            dp[i] = -1; 
+        } 
+        System.out.println(countWays(n, dp)); 
+    } 
+}
+
+//Time Complexity: O(n)
+//Auxiliary Space: O(n)