String Manipulation String Hash Map Counting Character Pattern Matching
Proficient Level

Implement the minimumWindowContainsPatternLength method that returns the length of the smallest substring containing all pattern characters.

The input contains two strings: text and pattern. Your task is to find the length of the smallest substring in text that contains every character required by pattern.

Characters must be counted correctly. For example, if the pattern contains two a characters, the selected window must also contain at least two a characters. If no valid substring exists, return 0.

Example 1
Input:
text (string) = ADOBECODEBANC
pattern (string) = ABC
Return:
(int) 4
Example 2
Input:
text (string) = a
pattern (string) = a
Return:
(int) 1
Example 3
Input:
text (string) = a
pattern (string) = aa
Return:
(int) 0

Use the sliding window technique with frequency counts.

First count how many times each character is required from pattern. Then expand the right side of the window over text and update the count of matched characters.

When the current window contains all required characters, try to shrink it from the left side. Each time the window is valid, update the minimum length.

Pseudocode:

function minimumWindowContainsPatternLength(text, pattern):
    if pattern is empty or text is shorter than pattern:
        return 0
    required = frequency map of pattern characters
    window = empty frequency map
    formed = 0
    need = number of unique characters in required
    left = 0
    best = infinity
    for right from 0 to length(text) - 1:
        add text[right] to window
        if text[right] count matches required count:
            formed++
        while formed == need:
            best = min(best, right - left + 1)
            remove text[left] from window
            if text[left] count becomes less than required count:
                formed--
            left++
    if best is infinity:
        return 0
    return best
Run your code to see the result.