package algs23;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac Quick.java
 *  Execution:    java Quick < input.txt
 *  Dependencies: StdOut.java StdIn.java
 *  Data files:   http://algs4.cs.princeton.edu/23quicksort/tiny.txt
 *                http://algs4.cs.princeton.edu/23quicksort/words3.txt
 *
 *  Sorts a sequence of strings from standard input using quicksort.
 *
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java Quick < tiny.txt
 *  A E E L M O P R S T X                 [ one string per line ]
 *
 *  % more words3.txt
 *  bed bug dad yes zoo ... all bad yet
 *
 *  % java Quick < words3.txt
 *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
 *
 *************************************************************************/

public class Quick {

  // quicksort the array
  public static <T extends Comparable<? super T>> void sort(T[] a) {
    StdRandom.shuffle(a);
    sort(a, 0, a.length - 1);
  }

  // quicksort the subarray from a[lo] to a[hi]
  private static <T extends Comparable<? super T>> void sort(T[] a, int lo, int hi) {
    if (hi <= lo) return;
    int j = partition(a, lo, hi);
    sort(a, lo, j-1);
    sort(a, j+1, hi);
    assert isSorted(a, lo, hi);
  }

  // partition the subarray a[lo .. hi] by returning an index j
  // so that a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
  private static <T extends Comparable<? super T>> int partition(T[] a, int lo, int hi) {
    int i = lo;
    int j = hi + 1;
    T v = a[lo];
    while (true) {

      // find item on lo to swap
      while (less(a[++i], v))
        if (i == hi) break;

      // find item on hi to swap
      while (less(v, a[--j]))
        if (j == lo) break;      // redundant since a[lo] acts as sentinel

      // check if pointers cross
      if (i >= j) break;

      exch(a, i, j);
    }

    // put v = a[j] into position
    exch(a, lo, j);

    // with a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
    return j;
  }

  /* *********************************************************************
   *  Rearranges the elements in a so that a[k] is the kth smallest element,
   *  and a[0] through a[k-1] are less than or equal to a[k], and
   *  a[k+1] through a[n-1] are greater than or equal to a[k].
   ***********************************************************************/
  public static <T extends Comparable<? super T>> T select(T[] a, int k) {
    if (k < 0 || k >= a.length) {
      throw new Error("Selected element out of bounds");
    }
    StdRandom.shuffle(a);
    int lo = 0, hi = a.length - 1;
    while (hi > lo) {
      int i = partition(a, lo, hi);
      if      (i > k) hi = i - 1;
      else if (i < k) lo = i + 1;
      else return a[i];
    }
    return a[lo];
  }



  /* *********************************************************************
   *  Helper sorting functions
   ***********************************************************************/

  // is v < w ?
  private static <T extends Comparable<? super T>> boolean less(T v, T w) {
    if (COUNT_OPS) DoublingTest.incOps ();
    return (v.compareTo(w) < 0);
  }

  // exchange a[i] and a[j]
  private static <T> void exch(T[] a, int i, int j) {
    if (COUNT_OPS) DoublingTest.incOps ();
    T swap = a[i];
    a[i] = a[j];
    a[j] = swap;
  }


  /* *********************************************************************
   *  Check if array is sorted - useful for debugging
   ***********************************************************************/
  private static <T extends Comparable<? super T>> boolean isSorted(T[] a) {
    return isSorted(a, 0, a.length - 1);
  }

  private static <T extends Comparable<? super T>> boolean isSorted(T[] a, int lo, int hi) {
    for (int i = lo + 1; i <= hi; i++)
      if (less(a[i], a[i-1])) return false;
    return true;
  }


  // print array to standard output
  private static <T> void show(T[] a) {
    for (T element : a) {
      StdOut.println(element);
    }
  }

  // test code
  private static boolean COUNT_OPS = false;
  public static void main(String[] args) {
    //String[] cards = In.readStrings ("data/cards.txt");
    //StdRandom.shuffle (cards);

    //StdIn.fromFile ("data/tiny.txt");
    //StdIn.fromFile ("data/cards.txt");
    StdIn.fromFile ("data/words3.txt");

    String[] a = StdIn.readAllStrings();
    sort(a);
    show(a);

    // display results again using select
    StdOut.println();
    for (int i = 0; i < a.length; i++) {
      String ith = select(a, i);
      StdOut.println(ith);
    }

    COUNT_OPS = true;
    DoublingTest.run (20000, 5, N -> ArrayGenerator.integerRandomUnique (N),          (Integer[] x) -> sort (x));
    DoublingTest.run (20000, 5, N -> ArrayGenerator.integerRandom (N, 2),             (Integer[] x) -> sort (x));
    DoublingTest.run (20000, 5, N -> ArrayGenerator.integerPartiallySortedUnique (N), (Integer[] x) -> sort (x));
  }

}