diff --git a/DIRECTORY.md b/DIRECTORY.md index 585c634c3429..37d9b3c295e2 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -816,6 +816,7 @@ - 📄 [Lower](src/main/java/com/thealgorithms/strings/Lower.java) - 📄 [Manacher](src/main/java/com/thealgorithms/strings/Manacher.java) - 📄 [MyAtoi](src/main/java/com/thealgorithms/strings/MyAtoi.java) + - 📄 [MoveHashToEnd](src/main/java/com/thealgorithms/strings/MoveHashToEnd.java) - 📄 [Palindrome](src/main/java/com/thealgorithms/strings/Palindrome.java) - 📄 [Pangram](src/main/java/com/thealgorithms/strings/Pangram.java) - 📄 [PermuteString](src/main/java/com/thealgorithms/strings/PermuteString.java) diff --git a/src/main/java/com/thealgorithms/strings/MoveHashToEnd.java b/src/main/java/com/thealgorithms/strings/MoveHashToEnd.java new file mode 100644 index 000000000000..bd686a0c5ba0 --- /dev/null +++ b/src/main/java/com/thealgorithms/strings/MoveHashToEnd.java @@ -0,0 +1,56 @@ +package com.thealgorithms.strings; + +/** + * Moves all '#' characters to the end of the given string while preserving + * the order of the other characters. + * + * Example: + * Input : "h#e#l#llo" + * Output : "helllo###" + * + * The algorithm works by iterating through the string and collecting + * all non-# characters first, then filling the remaining positions + * with '#'. + * + * Time Complexity: O(n) + * Space Complexity: O(n) + * + * @see Move all special characters to end - GeeksForGeeks + */ +public final class MoveHashToEnd { + + /** + * Private constructor to prevent instantiation of utility class. + */ + private MoveHashToEnd() { + } + + /** + * Moves all '#' characters in the input string to the end. + * + * @param str the input string containing characters and '#' + * @return a new string with all '#' characters moved to the end + */ + public static String moveHashToEnd(String str) { + if (str == null || str.isEmpty()) { + return str; + } + + char[] arr = str.toCharArray(); + int insertPos = 0; + + // Place all non-# characters at the beginning + for (char ch : arr) { + if (ch != '#') { + arr[insertPos++] = ch; + } + } + + // Fill remaining positions with '#' + while (insertPos < arr.length) { + arr[insertPos++] = '#'; + } + + return new String(arr); + } +} diff --git a/src/test/java/com/thealgorithms/strings/MoveHashToEndTest.java b/src/test/java/com/thealgorithms/strings/MoveHashToEndTest.java new file mode 100644 index 000000000000..016f72ff9d7f --- /dev/null +++ b/src/test/java/com/thealgorithms/strings/MoveHashToEndTest.java @@ -0,0 +1,54 @@ +package com.thealgorithms.strings; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertNull; + +import org.junit.jupiter.api.Test; + +public class MoveHashToEndTest { + + @Test + void testBasicCase() { + assertEquals("helllo###", MoveHashToEnd.moveHashToEnd("h#e#l#llo")); + } + + @Test + void testNoHash() { + assertEquals("hello", MoveHashToEnd.moveHashToEnd("hello")); + } + + @Test + void testAllHashes() { + assertEquals("###", MoveHashToEnd.moveHashToEnd("###")); + } + + @Test + void testHashAtEnd() { + assertEquals("hello#", MoveHashToEnd.moveHashToEnd("hello#")); + } + + @Test + void testHashAtStart() { + assertEquals("hello#", MoveHashToEnd.moveHashToEnd("#hello")); + } + + @Test + void testEmptyString() { + assertEquals("", MoveHashToEnd.moveHashToEnd("")); + } + + @Test + void testNullInput() { + assertNull(MoveHashToEnd.moveHashToEnd(null)); + } + + @Test + void testSingleHash() { + assertEquals("#", MoveHashToEnd.moveHashToEnd("#")); + } + + @Test + void testSingleNonHashChar() { + assertEquals("a", MoveHashToEnd.moveHashToEnd("a")); + } +}