separate the numbers implementation

codereview/beautifulNumberValidator.md

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+## Problem
+Adapted from [this HackerRank problem](https://www.hackerrank.com/challenges/separate-the-numbers/problem).
+
+[![Beautiful Number Description][1]][1]
+
+Instead of printing `YES` or `NO`, I just wanted to return a `boolean`.
+
+## Implementation
+
+<! -- language: lang-java -->
+
+    public class BeautifulNumberValidator {
+      public static boolean isValidBeautifulNumber(String s) {
+        if (s.length() < 2) {
+          return false;
+        }
+
+        for (int substringSize = 1; substringSize <= s.length() / 2; substringSize++) {
+          long value = Long.parseLong(s.substring(0, substringSize));
+
+          if (value == 0) {
+            break;
+          }
+
+          StringBuilder sb = new StringBuilder();
+          sb.append(value);
+
+          while (sb.length() < s.length() && sb.toString().equals(s.substring(0, sb.length()))) {
+            sb.append(++value);
+          }
+
+          if (sb.toString().equals(s)) {
+            return true;
+          }
+        }
+
+        return false;
+      }
+    }
+
+
+  [1]: https://i.stack.imgur.com/p8HI7.png

src/main/java/algorithms/implementations/BeautifulNumberValidatorImpl.java

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+package algorithms.implementations;
+
+import algorithms.interfaces.BeautifulNumberValidator;
+
+/**
+ * https://www.hackerrank.com/challenges/separate-the-numbers/problem
+ */
+
+public class BeautifulNumberValidatorImpl implements BeautifulNumberValidator {
+  @Override
+  public boolean isValidBeautifulNumber(final String s) {
+    if (s.length() < 2) {
+      return false;
+    }
+
+    for (int substringSize = 1; substringSize <= s.length() / 2; substringSize++) {
+      long value = Long.parseLong(s.substring(0, substringSize));
+
+      if (value == 0) {
+        break;
+      }
+
+      StringBuilder sb = new StringBuilder();
+      sb.append(value);
+
+      while (sb.length() < s.length() && sb.toString().equals(s.substring(0, sb.length()))) {
+        sb.append(++value);
+      }
+
+      if (sb.toString().equals(s)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+}

src/main/java/algorithms/interfaces/BeautifulNumberValidator.java

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+package algorithms.interfaces;
+
+public interface BeautifulNumberValidator {
+  boolean isValidBeautifulNumber(final String s);
+}

src/test/java/algorithms/implementations/BeautifulNumberValidatorImplTest.java

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+package algorithms.implementations;
+
+import algorithms.interfaces.BeautifulNumberValidator;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class BeautifulNumberValidatorImplTest {
+  final BeautifulNumberValidator validator = new BeautifulNumberValidatorImpl();
+
+  @Test
+  public void itShouldBeAValidBeautifulNumber() {
+    assertTrue(validator.isValidBeautifulNumber("1234"));
+  }
+
+  @Test
+  public void itShouldNotBeAValidBeautifulNumber() {
+    assertFalse(validator.isValidBeautifulNumber("101103"));
+  }
+
+  @Test
+  public void itShouldNotBeAValidBeautifulNumberSinceItStartsWithZero() {
+    assertFalse(validator.isValidBeautifulNumber("010203"));
+  }
+
+  @Test
+  public void itShouldNotBeAValidBeautifulNumberSinceItIsTooSmall() {
+    assertFalse(validator.isValidBeautifulNumber("1"));
+  }
+}