Added isogram utility class and unit tests (#6594)

* added isogram utility class and unit tests Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * checking lint issue Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * linter fix Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * fix: HideUtilityClassConstructor Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * linter fix Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * updated isogram class to final Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * pipeline bug fixing Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> * renamed function names and few fixes w.r.t to suggestion Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com> --------- Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com>
2025-12-19 07:00:35 +08:00 · 2025-10-03 17:03:12 +05:30
parent 8d14b492fd
commit 7e29be3ad8
2 changed files with 209 additions and 0 deletions
--- a/src/main/java/com/thealgorithms/strings/Isogram.java
+++ b/src/main/java/com/thealgorithms/strings/Isogram.java
@@ -0,0 +1,92 @@
+package com.thealgorithms.strings;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * An isogram (also called heterogram or nonpattern word) is a word in which no
+ * letter of the word occurs more than once. Each character appears exactly
+ * once.
+ *
+ * For example, the word "uncopyrightable" is the longest common English isogram
+ * with 15 unique letters. Other examples include "dermatoglyphics" (15
+ * letters),
+ * "background" (10 letters), "python" (6 letters), and "keyboard" (8 letters).
+ * But words like "hello" and "programming" are not isograms because some
+ * letters
+ * appear multiple times ('l' appears twice in "hello", while 'r', 'm', 'g'
+ * repeat
+ * in "programming").
+ *
+ * Isograms are particularly valuable in creating substitution ciphers and are
+ * studied in recreational linguistics. A perfect pangram, which uses all 26
+ * letters
+ * of the alphabet exactly once, is a special type of isogram.
+ *
+ * Reference from https://en.wikipedia.org/wiki/Heterogram_(literature)#Isograms
+ */
+public final class Isogram {
+    /**
+     * Private constructor to prevent instantiation of utility class.
+     */
+    private Isogram() {
+    }
+
+    /**
+     * Checks if a string is an isogram using boolean array approach.
+     *
+     * Time Complexity: O(n)
+     * Space Complexity: O(1)
+     *
+     * @param str the input string
+     * @return true if the string is an isogram, false otherwise
+     * @throws IllegalArgumentException if the string contains non-alphabetic
+     *                                  characters
+     */
+    public static boolean isAlphabeticIsogram(String str) {
+        if (str == null || str.isEmpty()) {
+            return true;
+        }
+
+        str = str.toLowerCase();
+
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            if (ch < 'a' || ch > 'z') {
+                throw new IllegalArgumentException("Input contains non-alphabetic character: '" + ch + "'");
+            }
+        }
+
+        boolean[] seenChars = new boolean[26];
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            int index = ch - 'a';
+            if (seenChars[index]) {
+                return false;
+            }
+            seenChars[index] = true;
+        }
+        return true;
+    }
+
+    /**
+     * Checks if a string is an isogram using length comparison approach.
+     * Time Complexity: O(n)
+     * Space Complexity: O(k) where k is the number of unique characters
+     *
+     * @param str the input string
+     * @return true if the string is an isogram, false otherwise
+     */
+    public static boolean isFullIsogram(String str) {
+        if (str == null || str.isEmpty()) {
+            return true;
+        }
+        str = str.toLowerCase();
+
+        Set<Character> uniqueChars = new HashSet<>();
+        for (char ch : str.toCharArray()) {
+            uniqueChars.add(ch);
+        }
+        return uniqueChars.size() == str.length();
+    }
+}