Java/src/main/java/com/thealgorithms/strings/Isogram.java at master · aroonkumar/Java · GitHub

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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();

}

Java/src/main/java/com/thealgorithms/strings/Isogram.java at master · aroonkumar/Java · GitHub

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