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public class Solution {
    public boolean checkInclusion(String s1, String s2) {
        int n = s2.length(), k = s1.length();
        if (k > n) return false;

        // Frequency count for s1
        int[] freqS1 = new int[26];
        for (char c : s1.toCharArray()) {
            freqS1[c - 'a']++;
        }

        // Sliding window frequency count for s2
        int[] freqWindow = new int[26];
        int i = 0, j = 0;

        // Process the first k elements
        while (j < k) {
            freqWindow[s2.charAt(j) - 'a']++;
            j++;
        }

        // Compare the first window
        if (matches(freqS1, freqWindow)) return true;

        // Slide the window
        while (j < n) {
            freqWindow[s2.charAt(j) - 'a']++; // Add the new character
            freqWindow[s2.charAt(i) - 'a']--; // Remove the old character
            j++;
            i++;

            // Check if current window matches
            if (matches(freqS1, freqWindow)) return true;
        }

        return false;
    }

    // Helper function to compare two frequency arrays
    private boolean matches(int[] freqS1, int[] freqWindow) {
        for (int i = 0; i < 26; i++) {
            if (freqS1[i] != freqWindow[i]) return false;
        }
        return true;
    }
}