class Solution:
    def checkInclusion(self, s1: str, s2: str) -> bool:
        if len(s1) > len(s2):
            return False
        
        # Initialize frequency arrays for a-z
        s1_count = [0] * 26
        s2_count = [0] * 26
        
        # Fill frequency arrays for the first window
        for i in range(len(s1)):
            s1_count[ord(s1[i]) - ord('a')] += 1
            s2_count[ord(s2[i]) - ord('a')] += 1
            
        # Check the very first window
        if s1_count == s2_count:
            return True
            
        # Slide the window across s2
        # i represents the index of the character entering the window
        for i in range(len(s1), len(s2)):
            # Add the new character to the window
            s2_count[ord(s2[i]) - ord('a')] += 1
            
            # Remove the character that just left the window
            # The character leaving is at index: i - len(s1)
            left_char_idx = i - len(s1)
            s2_count[ord(s2[left_char_idx]) - ord('a')] -= 1
            
            # Check if the current window matches s1
            if s1_count == s2_count:
                return True
                
        return False