// 闲言少许，直奔主题，我是宋鹏举。

import java.io.PrintStream;public class RollingHash{  private static final int R = 31;  private int _hash;  private int _rK;  private CharSequence _c;  private int _k;  private int _offset;    public RollingHash(int k)  {    if (k <= 0) {      throw new IllegalArgumentException("k must be positive");    }    this._k = k;        this._rK = 1;    for (int i = 1; i < k; i++) {      this._rK *= 31;    }  }    public void init(CharSequence c)  {    if (this._k > c.length()) {      throw new IllegalArgumentException("k is greater then lenght of content");    }    this._c = c;    this._offset = 0;        this._hash = 0;    for (int i = 0; i < this._k; i++) {      this._hash = (this._hash * 31 + this._c.charAt(i));    }  }    public boolean hasNext()  {    if (this._offset + this._k >= this._c.length()) {      return false;    }    return true;  }    public int next()  {    if (this._offset + this._k >= this._c.length()) {      throw new IllegalStateException("Past the end of content.");    }    int currentHash = this._hash;        this._hash = ((this._hash - this._rK * this._c.charAt(this._offset)) * 31 + this._c.charAt(this._offset + this._k));        this._offset += 1;        return currentHash;  }    public static void main(String[] args)  {    String text = "01234567890123456789012345678901234567890123456789testesteskdjfgdkfjghdkfjghdkfjghdkjgh";        int k = 20;        RollingHash rh = new RollingHash(k);    rh.init(text);    for (int i = 0; rh.hasNext(); i++) {      System.out.println("Hash " + i + ": " + rh.next());    }  }}