Solution.java

class Solution {
    public int equalCountSubstrings(String s, int count) {
        int ans = 0;
        int[] cnt = new int[26];
        int n = s.length();
        for (int i = 1; i < 27 && i * count <= n; ++i) {
            int k = i * count;
            Arrays.fill(cnt, 0);
            int t = 0;
            for (int j = 0; j < n; ++j) {
                int a = s.charAt(j) - 'a';
                ++cnt[a];
                t += cnt[a] == count ? 1 : 0;
                t -= cnt[a] == count + 1 ? 1 : 0;
                if (j - k >= 0) {
                    int b = s.charAt(j - k) - 'a';
                    --cnt[b];
                    t += cnt[b] == count ? 1 : 0;
                    t -= cnt[b] == count - 1 ? 1 : 0;
                }
                ans += i == t ? 1 : 0;
            }
        }
        return ans;
    }
}