Create DavidsStarcase.java

Author: Foxeyyy

DavidsStarcase.java

@@ -0,0 +1,50 @@
+import java.io.*;
+import java.math.*;
+import java.security.*;
+import java.text.*;
+import java.util.*;
+import java.util.concurrent.*;
+import java.util.regex.*;
+
+public class Solution {
+
+    //Bottom-up O(n) space and time
+    static int stepPerms(int n) {
+
+        int[] memo = new int[n+1];
+
+        for (int i = 0; i <= n; i++) {
+            if (i == 0) memo[0] = 0;
+            else if (i == 1) memo[1] = 1;
+            else if (i == 2) memo[2] = 2;
+            else if (i == 3) memo[3] = 4;
+            else memo[i] = memo[i-1] + memo[i-2] + memo[i-3];
+        }
+
+        return memo[n];
+        
+    }
+
+    private static final Scanner scanner = new Scanner(System.in);
+
+    public static void main(String[] args) throws IOException {
+        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
+
+        int s = scanner.nextInt();
+        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
+
+        for (int sItr = 0; sItr < s; sItr++) {
+            int n = scanner.nextInt();
+            scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
+
+            int res = stepPerms(n);
+
+            bufferedWriter.write(String.valueOf(res));
+            bufferedWriter.newLine();
+        }
+
+        bufferedWriter.close();
+
+        scanner.close();
+    }
+}