字符串哈希+定长滑动窗口

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.HashSet;

public class Main {
    static final int P = 131;
    static long[] h = new long[(int) 2e5 + 10]; //存哈希值
    static long[] p = new long[(int) 2e5 + 10]; //存P的i次幂
    static String H;

    static void init(int len) { //预处理哈希值
        p[0] = 1;
        h[0] = 0;
        for (int i = 1; i < len; ++i) {
            p[i] = P * p[i - 1];
            h[i] = (h[i - 1] * P + H.charAt(i)) % (Long.MAX_VALUE);
        }
    }

    static long calc(int l, int r) { //计算区间哈希值
        return h[r] - h[l - 1] * p[r - l + 1];
    }

    static void solve() throws IOException {
        String N = " " + br.readLine();
        H = " " + br.readLine();
        int n = N.length() - 1;
        int m = H.length() - 1;
        init(H.length());
        HashSet<Long> set = new HashSet<>(); 
        int[] cnt = new int[30]; 
        for (int i = 1; i <= n; ++i) {
            cnt[N.charAt(i) - 'a']++; 
        }
        int t = 0;
        for (int i = 0; i < 26; ++i) {
            if (cnt[i] == 0) { 
                t++;
            }
        }
        for (int i = 1; i <= m; ++i) {
            int x = H.charAt(i) - 'a';
            cnt[x]--;
            if (cnt[x] == 0) {
                t++;
            } else if (cnt[x] == -1) {
                t--;
            }
            if (i > n) {
                int s = H.charAt(i - n) - 'a';
                cnt[s]++;
                if (cnt[s] == 0) {
                    t++;
                } else if (cnt[s] == 1) {
                    t--;
                }
            }
            if (t == 26) {
                set.add(calc(i - n + 1, i));
            }
        }
        pw.print(set.size());
    }

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static PrintWriter pw = new PrintWriter(new OutputStreamWriter(System.out));

    public static void main(String[] args) throws IOException {
        int t = 1;
        while (t-- > 0) {
            solve();
        }
        pw.close();
    }
}