Smallest window that contains all characters of string itself

Given a string str, find the smallest window length that contains all the characters of the given string at least one time.

Examples:

Input: str = "aabcbcdbca"
Output: 4
Explanation: Sub-string -> "dbca"

Input: str = "aaab"
Output: 2
Explanation: Sub-string -> "ab"

[Naive Approach] - Generating All Substrings - O(n ^ 2) Time and O(1) Space

• Use a count array to identify all the unique characters in the string.
• Generate substrings using two pointers and track characters using a visited array.
• Check whether the current substring contains all distinct characters.
• If it does, update the minimum length of the substring found so far.

4

[Expected Approach] - Using Sliding Window - O(n) Time and O(1) Space

• Count total distinct characters in the string using a visited array.
• Use a sliding window with two pointers (start and i) to expand the window and include characters.
• Track character frequencies in the window using cur[] and update cnt when a new distinct character appears.
• When the window contains all distinct characters, shrink it from the left and update the minimum window length.

4

Related Article:

• Length of the smallest sub-string consisting of maximum distinct characters
• Smallest window in a String containing all characters of other String