/*************************************************************************
 *  Compilation:  javac Quick3way.java
 *  Execution:    java Quick3way < 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 3-way quicksort.
 *   
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java Quick3way < 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 Quick3way < words3.txt
 *  all bad bed bug dad ... yes yet zoo    [ one string per line ]
 *
 *************************************************************************/

public class Quick3way {

    // quicksort the array a[] using 3-way partitioning
    public static void sort(Comparable[] a) {
        sort(a, 0, a.length - 1);
        assert isSorted(a);
    }

    // quicksort the subarray a[lo .. hi] using 3-way partitioning
    private static void sort(Comparable[] a, int lo, int hi) { 
        if (hi <= lo) return;
        int lt = lo, gt = hi;
        Comparable v = a[lo];
        int i = lo;
        while (i <= gt) {
            int cmp = a[i].compareTo(v);
            if      (cmp < 0) exch(a, lt++, i++);
            else if (cmp > 0) exch(a, i, gt--);
            else              i++;
        }

        // a[lo..lt-1] < v = a[lt..gt] < a[gt+1..hi]. 
        sort(a, lo, lt-1);
        sort(a, gt+1, hi);
        assert isSorted(a, lo, hi);
    }



   /***********************************************************************
    *  Helper sorting functions
    ***********************************************************************/
    
    // is v < w ?
    private static boolean less(Comparable v, Comparable w) {
        return (v.compareTo(w) < 0);
    }

    // does v == w ?
    private static boolean eq(Comparable v, Comparable w) {
        return (v.compareTo(w) == 0);
    }
        
    // exchange a[i] and a[j]
    private static void exch(Object[] a, int i, int j) {
        Object swap = a[i];
        a[i] = a[j];
        a[j] = swap;
    }


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

    private static boolean isSorted(Comparable[] 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 void show(Comparable[] a) {
        for (int i = 0; i < a.length; i++) {
            StdOut.println(a[i]);
        }
    }

    // Read strings from standard input, sort them, and print.
    public static void main(String[] args) {
        String[] a = StdIn.readStrings();
        Quick3way.sort(a);
        show(a);
    }

}
