Recursive digit sum done

Author: rampatra

src/main/java/com/hackerrank/algorithms/recursion/RecursiveDigitSum.java

@@ -0,0 +1,60 @@
+package com.hackerrank.algorithms.recursion;
+
+import java.io.BufferedWriter;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.Scanner;
+
+/**
+ * Recursive Digit Sum Problem.
+ *
+ * @link https://www.hackerrank.com/challenges/recursive-digit-sum/problem
+ * @author rpatra16
+ * @since 06/11/2018
+ */
+public class RecursiveDigitSum {
+
+    /**
+     * Finds the recursive digit sum of n.
+     *
+     * @param n number
+     * @param k the number would be repeated k times
+     * @return recursive sum of the digits
+     */
+    private static int superDigit(String n, int k) {
+        if (n.length() == 1 && k == 0) {
+            return Integer.parseInt(n);
+        }
+
+        Long sum = 0L;
+        char[] num = n.toCharArray();
+        for (int i = 0; i < num.length; i++) {
+            sum += Long.parseLong(String.valueOf(num[i]));
+        }
+
+        if (k != 0) sum *= k;
+
+        return superDigit(sum.toString(), 0);
+    }
+
+    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")));
+
+        String[] nk = scanner.nextLine().split(" ");
+
+        String n = nk[0];
+
+        int k = Integer.parseInt(nk[1]);
+
+        int result = superDigit(n, k);
+
+        bufferedWriter.write(String.valueOf(result));
+        bufferedWriter.newLine();
+
+        bufferedWriter.close();
+
+        scanner.close();
+    }
+}