Add time and space complexity documentation to LongestNonRepetitiveSubstring

Author: eMohan07

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

@@ -5,6 +5,10 @@
 
 /**
  * Class for finding the length of the longest substring without repeating characters.
+ *
+ * <p>This implementation uses the sliding window technique combined with a
+ * {@link java.util.HashMap} to track the last seen index of each character
+ * while iterating through the string.</p>
  */
 final class LongestNonRepetitiveSubstring {
     private LongestNonRepetitiveSubstring() {
@@ -13,6 +17,21 @@ private LongestNonRepetitiveSubstring() {
     /**
      * Finds the length of the longest substring without repeating characters.
      *
+     * <p>The algorithm maintains a sliding window defined by two pointers.
+     * As we iterate through the string, we expand the window and update the
+     * starting position whenever a duplicate character is encountered within
+     * the current window.</p>
+     *
+     * <p><b>Time Complexity:</b> O(n), where n is the length of the input string.
+     * Each character is processed at most once.</p>
+     *
+     * <p><b>Space Complexity:</b> O(min(n, m)), where:
+     * <ul>
+     *   <li>n = length of the input string</li>
+     *   <li>m = size of the character set (e.g., 128 for ASCII)</li>
+     * </ul>
+     * The additional space is used to store character indices in the HashMap.</p>
+     *
      * @param s the input string
      * @return the length of the longest non-repetitive substring
      */
@@ -39,4 +58,4 @@ public static int lengthOfLongestSubstring(String s) {
 
         return maxLength;
     }
-}
+}