Array String Hash Map Sliding Window
Intermediate Level

Implement the permutationInStringCheck method that checks whether the text contains any permutation of the pattern.

The input contains two strings: pattern and text. Your task is to check whether any permutation of pattern appears as a continuous substring inside text.

A permutation uses exactly the same characters with the same frequencies, but the order can be different.

For example, ab appears as the permutation ba inside eidbaooo, so the answer is true.

Example 1
Input:
pattern (string) = ab
text (string) = eidbaooo
Return:
(boolean) true
Example 2
Input:
pattern (string) = ab
text (string) = eidboaoo
Return:
(boolean) false
Example 3
Input:
pattern (string) = a
text (string) = a
Return:
(boolean) true

Use a sliding window whose length is the same as pattern.

Build the character frequency count for pattern. Then move a same-sized window across text and maintain the character count of the current window.

If both frequency counts match at any point, the current window is a permutation of pattern.

Pseudocode:

function permutationInStringCheck(pattern, text):
    m = length of pattern
    n = length of text
    if m > n:
        return false
    patternCount = frequency count of pattern
    windowCount = frequency count of first m characters of text
    if windowCount == patternCount:
        return true
    for right from m to n - 1:
        add text[right] to windowCount
        leftChar = text[right - m]
        remove one count of leftChar from windowCount
        if windowCount == patternCount:
            return true
    return false
Run your code to see the result.