image.png

解法

class Solution {
    public boolean checkInclusion(String s1, String s2) {
        if (s1.length() > s2.length()) {
            return false;
        }
        int[] count1 = new int[26];
        int[] count2 = new int[26];
        int n = s1.length();
        for (int i = 0; i < n; i++) {
            count1[s1.charAt(i) - 'a']++;
            count2[s2.charAt(i) - 'a']++;
        }   
        if (Arrays.equals(count1, count2)) {
            return true;
        }
        for (int i = n; i < s2.length(); i++) {
            count2[s2.charAt(i) - 'a']++;
            count2[s2.charAt(i - n) - 'a']--;
            if (Arrays.equals(count1, count2)) {
                return true;
            }            
        }
        return false;
    }
}