Update longest_substr_no_char_repeats.md

Author: ratulb

docs/longest_substr_no_char_repeats.md

@@ -2,28 +2,51 @@
 
 
 ```python
+from collections import Set
+
+# Function to compute the length of the longest substring without repeating characters.
+# Takes a StringLiteral `s` and returns an unsigned 16-bit integer.
 fn len_longest_substr_no_char_repeats(s: StringLiteral) raises -> UInt16:
+    # If the input string is empty, return 0 immediately
     if len(s) == 0:
         return 0
+
+    # Initialize a Set to keep track of characters in the current window (substring)
+    # Start by adding the first character of the string
     seen = Set(s[0])
+
+    # `left` is the left boundary of the current sliding window (start index)
     left = 0
+
+    # Initial max_length is 1 since we already have one character in the set
     max_length = 1
+
+    # Start iterating from the second character to the end of the string
     for idx in range(1, len(s)):
+        # If the current character is already in the set, it means a repetition
+        # So we move the `left` boundary forward until we remove the duplicate
         while s[idx] in seen:
             seen.remove(s[left])
             left += 1
+
+        # Add the current character to the set
         seen.add(s[idx])
+
+        # Update max_length with the size of the current window (set size)
         max_length = max(max_length, len(seen))
+
+    # Return the maximum length found
     return max_length
 
 
 fn main() raises:
     s = "abcabcbb"
-    print(len_longest_substr_no_char_repeats(s))
+    print(len_longest_substr_no_char_repeats(s))  # 3
     s = "bbbbb"
-    print(len_longest_substr_no_char_repeats(s))
+    print(len_longest_substr_no_char_repeats(s))  # 1
     s = "pwwkew"
-    print(len_longest_substr_no_char_repeats(s))
+    print(len_longest_substr_no_char_repeats(s))  # 3
+
 ```