feat: climbing-stairs solution

Author: sm9171

climbing-stairs/sm9171.java

@@ -0,0 +1,16 @@
+class Solution {
+    public int climbStairs(int n) {
+        int[] memo = new int[n+1];
+        return recur(n, memo);
+    }
+
+    public static int recur(int n, int[] memo) {
+        if (n < 0) return 0;
+        if (n == 0) return 1;
+
+        if (memo[n] > 0) return memo[n];
+
+        memo[n] = recur(n - 1, memo) + recur(n - 2, memo);
+        return memo[n];
+    }
+}