Add 408 Valid Word Abbreviation with unit tests

Author: FreeTymeKiyan

src/main/java/com/freetymekiyan/algorithms/level/easy/ValidWordAbbreviation.java

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+package com.freetymekiyan.algorithms.level.easy;
+
+/**
+ * 408. Valid Word Abbreviation
+ * <p>
+ * Given a non-empty string s and an abbreviation abbr, return whether the string matches with the given abbreviation.
+ * <p>
+ * A string such as "word" contains only the following valid abbreviations:
+ * <p>
+ * ["word", "1ord", "w1rd", "wo1d", "wor1", "2rd", "w2d", "wo2", "1o1d", "1or1", "w1r1", "1o2", "2r1", "3d", "w3", "4"]
+ * <p>
+ * Notice that only the above abbreviations are valid abbreviations of the string "word". Any other string is not a
+ * valid abbreviation of "word".
+ * <p>
+ * Note:
+ * Assume s contains only lowercase letters and abbr contains only lowercase letters and digits.
+ * <p>
+ * Example 1:
+ * Given s = "internationalization", abbr = "i12iz4n":
+ * Return true.
+ * <p>
+ * Example 2:
+ * Given s = "apple", abbr = "a2e":
+ * Return false.
+ * <p>
+ * Related Topics: String
+ * <p>
+ * Companies: Google
+ * <p>
+ * Similar Problems: Minimum Unique Word Abbreviation (H), Word Abbreviation (H)
+ */
+public class ValidWordAbbreviation {
+
+  /**
+   * Word and abbreviation don't match if:
+   * <ol>
+   *   <li>The lengths are different</li>
+   *   <li>The actual characters at specific positions are different</li>
+   * </ol>
+   * So iterate through abbreviation, track the position and compare the characters.
+   * If there is a number, find the full number first then update indices.
+   * The number abbreviates that many characters.
+   * <p>
+   * If there's no number, just compare the characters.
+   * <p>
+   * Both indices should be at the ends if it's a perfect match.
+   */
+  public boolean validWordAbbreviation(String word, String abbr) {
+    if (word == null && abbr == null) {
+      return true;
+    }
+    if (word == null || abbr == null) {
+      return false;
+    }
+    int pWord = 0;
+    int pAbbr = 0;
+    while (pWord < word.length() && pAbbr < abbr.length()) {
+      int end = pAbbr;
+      while (end < abbr.length() && '0' <= abbr.charAt(end) && abbr.charAt(end) <= '9') {
+        end++;
+      }
+      if (end == pAbbr) { // No number, compare characters
+        if (abbr.charAt(pAbbr) != word.charAt(pWord)) {
+          return false;
+        }
+        pAbbr++;
+        pWord++;
+      } else {
+        if (abbr.charAt(pAbbr) == '0') { // Edge case: should not have leading zero
+          return false;
+        }
+        final int abbreviated = Integer.parseInt(abbr.substring(pAbbr, end));
+        pWord += abbreviated;
+        pAbbr = end;
+      }
+    }
+    return pWord == word.length() && pAbbr == abbr.length();
+  }
+}

src/test/java/com/freetymekiyan/algorithms/level/easy/ValidWordAbbreviationTest.java

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+package com.freetymekiyan.algorithms.level.easy;
+
+import org.testng.Assert;
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+public class ValidWordAbbreviationTest {
+
+  @DataProvider
+  public Object[][] getExamples() {
+    return new Object[][]{
+        new Object[]{null, null, true},
+        new Object[]{null, "", false},
+        new Object[]{"", null, false},
+        new Object[]{"internationalization", "i12iz4n", true},
+        new Object[]{"apple", "a2e", false},
+        new Object[]{"apple", "0a2e", false} // Edge case: leading zeros
+    };
+  }
+
+  @Test(dataProvider = "getExamples")
+  public void testValidWordAbbreviation(String word, String abbr, boolean expected) {
+    final boolean actual = new ValidWordAbbreviation().validWordAbbreviation(word, abbr);
+    Assert.assertEquals(actual, expected);
+  }
+}