Merge branch 'master' into add-factorial-recursion

Author: DenizAltunkapan

src/main/java/com/thealgorithms/sorts/QuickSort.java

@@ -1,24 +1,36 @@
 package com.thealgorithms.sorts;
 
 /**
- * @author Varun Upadhyay (https://github.com/varunu28)
- * @author Podshivalov Nikita (https://github.com/nikitap492)
+ * QuickSort is a divide-and-conquer sorting algorithm.
+ *
+ * <p>The algorithm selects a pivot element and partitions the array into two
+ * subarrays such that:
+ * <ul>
+ *   <li>Elements smaller than the pivot are placed on the left</li>
+ *   <li>Elements greater than the pivot are placed on the right</li>
+ * </ul>
+ *
+ * <p>The subarrays are then recursively sorted until the entire array is ordered.
+ *
+ * <p>This implementation uses randomization to reduce the probability of
+ * encountering worst-case performance on already sorted inputs.
+ *
+ * <p>Time Complexity:
+ * <ul>
+ *   <li>Best Case: O(n log n)</li>
+ *   <li>Average Case: O(n log n)</li>
+ *   <li>Worst Case: O(n^2)</li>
+ * </ul>
+ *
+ * <p>Space Complexity: O(log n) due to recursion stack (in-place sorting).
+ *
+ * @author Varun Upadhyay
+ * @author Podshivalov Nikita
  * @see SortAlgorithm
  */
+
 class QuickSort implements SortAlgorithm {
 
-    /**
-     * Generic Quick Sort algorithm.
-     *
-     * Time Complexity:
-     * - Best case: O(n log n) – pivot splits array roughly in half each time.
-     * - Average case: O(n log n)
-     * - Worst case: O(n^2) – occurs when pivot consistently produces unbalanced splits.
-     *
-     * Space Complexity: O(log n) – recursion stack, in-place sorting.
-     *
-     * @see SortAlgorithm
-     */
     @Override
     public <T extends Comparable<T>> T[] sort(T[] array) {
         doSort(array, 0, array.length - 1);
@@ -28,27 +40,33 @@ public <T extends Comparable<T>> T[] sort(T[] array) {
     /**
      * The sorting process
      *
-     * @param left The first index of an array
-     * @param right The last index of an array
      * @param array The array to be sorted
+     * @param left  The first index of an array
+     * @param right The last index of an array
      */
     private static <T extends Comparable<T>> void doSort(T[] array, final int left, final int right) {
+        // Continue sorting only if the subarray has more than one element
         if (left < right) {
+            // Randomly choose a pivot and partition the array
             final int pivot = randomPartition(array, left, right);
+            // Recursively sort elements before the pivot
             doSort(array, left, pivot - 1);
+            // Recursively sort elements after the pivot
             doSort(array, pivot, right);
         }
     }
 
     /**
-     * Randomize the array to avoid the basically ordered sequences
+     * Randomizes the array to avoid already ordered or nearly ordered sequences
      *
      * @param array The array to be sorted
-     * @param left The first index of an array
+     * @param left  The first index of an array
      * @param right The last index of an array
      * @return the partition index of the array
      */
     private static <T extends Comparable<T>> int randomPartition(T[] array, final int left, final int right) {
+        // Randomizing the pivot helps avoid worst-case performance
+        // for already sorted or nearly sorted arrays
         final int randomIndex = left + (int) (Math.random() * (right - left + 1));
         SortUtils.swap(array, randomIndex, right);
         return partition(array, left, right);
@@ -58,21 +76,26 @@ private static <T extends Comparable<T>> int randomPartition(T[] array, final in
      * This method finds the partition index for an array
      *
      * @param array The array to be sorted
-     * @param left The first index of an array
-     * @param right The last index of an array Finds the partition index of an
-     * array
+     * @param left  The first index of an array
+     * @param right The last index of an array
      */
     private static <T extends Comparable<T>> int partition(T[] array, int left, int right) {
         final int mid = (left + right) >>> 1;
+        // Choose the middle element as the pivot
         final T pivot = array[mid];
-
+        // Move the left and right pointers towards each other
         while (left <= right) {
+            // Move left pointer until an element >= pivot is found
             while (SortUtils.less(array[left], pivot)) {
                 ++left;
             }
+
+            // Move right pointer until an element <= pivot is found
             while (SortUtils.less(pivot, array[right])) {
                 --right;
             }
+
+            // Swap elements that are on the wrong side of the pivot
             if (left <= right) {
                 SortUtils.swap(array, left, right);
                 ++left;

src/main/java/com/thealgorithms/strings/LengthOfLastWord.java

@@ -0,0 +1,51 @@
+package com.thealgorithms.strings;
+
+/**
+ * The {@code LengthOfLastWord} class provides a utility method to determine
+ * the length of the last word in a given string.
+ *
+ * <p>A "word" is defined as a maximal substring consisting of non-space
+ * characters only. Trailing spaces at the end of the string are ignored.
+ *
+ * <p><strong>Example:</strong>
+ * <pre>{@code
+ * LengthOfLastWord obj = new LengthOfLastWord();
+ * System.out.println(obj.lengthOfLastWord("Hello World"));  // Output: 5
+ * System.out.println(obj.lengthOfLastWord("  fly me   to   the moon  "));  // Output: 4
+ * System.out.println(obj.lengthOfLastWord("luffy is still joyboy"));  // Output: 6
+ * }</pre>
+ *
+ * <p>This implementation runs in O(n) time complexity, where n is the length
+ * of the input string, and uses O(1) additional space.
+ */
+public class LengthOfLastWord {
+
+    /**
+     * Returns the length of the last word in the specified string.
+     *
+     * <p>The method iterates from the end of the string, skipping trailing
+     * spaces first, and then counts the number of consecutive non-space characters
+     * characters until another space (or the beginning of the string) is reached.
+     *
+     * @param s the input string to analyze
+     * @return the length of the last word in {@code s}; returns 0 if there is no word
+     * @throws NullPointerException if {@code s} is {@code null}
+     */
+    public int lengthOfLastWord(String s) {
+        int sizeOfString = s.length() - 1;
+        int lastWordLength = 0;
+
+        // Skip trailing spaces from the end of the string
+        while (sizeOfString >= 0 && s.charAt(sizeOfString) == ' ') {
+            sizeOfString--;
+        }
+
+        // Count the characters of the last word
+        while (sizeOfString >= 0 && s.charAt(sizeOfString) != ' ') {
+            lastWordLength++;
+            sizeOfString--;
+        }
+
+        return lastWordLength;
+    }
+}

src/test/java/com/thealgorithms/strings/LengthOfLastWordTest.java

@@ -0,0 +1,18 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class LengthOfLastWordTest {
+    @Test
+    public void testLengthOfLastWord() {
+        assertEquals(5, new LengthOfLastWord().lengthOfLastWord("Hello World"));
+        assertEquals(4, new LengthOfLastWord().lengthOfLastWord("  fly me   to   the moon  "));
+        assertEquals(6, new LengthOfLastWord().lengthOfLastWord("luffy is still joyboy"));
+        assertEquals(5, new LengthOfLastWord().lengthOfLastWord("Hello"));
+        assertEquals(0, new LengthOfLastWord().lengthOfLastWord("     "));
+        assertEquals(0, new LengthOfLastWord().lengthOfLastWord(""));
+        assertEquals(3, new LengthOfLastWord().lengthOfLastWord("JUST LIE  "));
+    }
+}