001
002
003
004
005
006
007
008
009
010
011
012
013
014
015
016
017
018
019
020
021
022
023
024
025
026
027
028
029
030
031
032
033
034
035
036
037
038
039
040
041
042
043
044
045
046
047
048
049
050
051
052
053
054
055
056
057
058
059
060
061
062
063
064
065
066
067
068
069
070
071
072
073
074
075
076
077
078
079
080
081
082
083
084
085
086
087
088
089
090
091
092
093
094
095
096
097
098
099
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
package algs51; // section 5.1
import stdlib.*;
/* *********************************************************************************
 *  Compilation: javac Quick3string.java
 *  Execution:   java Quick3string < input.txt
 *
 *  Reads string from standard input and 3-way string quicksort them.
 *
 *  WARNING: This program assumes that the <tt>substring()</tt> method takes
 *  constant time and space. Beginning with Oracle / OpenJDK Java 7, Update 6,
 *  the substring method takes linear time and space in the size of the
 *  extracted substring. Do NOT use this code with such versions.
 *
 *  To fix: replace less() with a version that uses charAt().
 *
 *  PATCH HAS BEEN APPLIED HERE: See less() versus less1() below.
 *
 *  % java Quick3string < shell.txt
 *  are
 *  by
 *  sea
 *  seashells
 *  seashells
 *  sells
 *  sells
 *  she
 *  she
 *  shells
 *  shore
 *  surely
 *  the
 *  the
 *
 * MAX_LENGTH = 64
 * RESULTS WITH Arrays.sort (Mergesort)
 *
 *     $ ./runjava algs51.Quick3string
 *       256000 [0.282 0.876]
 *       512000 [0.384 1.362]
 *      1024000 [0.839 2.185]
 *     $ ./runjava algs51.Quick3string
 *       256000 [0.291 1.003]
 *       512000 [0.380 1.306]
 *      1024000 [0.880 2.316]
 *     $ ./runjava algs51.Quick3string
 *       256000 [0.243 0.721]
 *       512000 [0.396 1.630]
 *      1024000 [0.846 2.136]
 *
 * RESULTS with Quick3string (with less implemented using charAt)
 *
 *     $ ./runjava  algs51.Quick3string
 *       256000 [0.108 1.714]
 *       512000 [0.248 2.296]
 *      1024000 [0.567 2.286]
 *     $ ./runjava  algs51.Quick3string
 *       256000 [0.104 1.576]
 *       512000 [0.250 2.404]
 *      1024000 [0.605 2.420]
 *     $ ./runjava  algs51.Quick3string
 *       256000 [0.110 1.746]
 *       512000 [0.261 2.373]
 *      1024000 [0.589 2.257]
 *
 * RESULTS with Quick3string (with less implemented using substring)
 *
 *     $ ./runjava  algs51.Quick3string
 *       256000 [0.251 0.815]
 *       512000 [0.422 1.681]
 *      1024000 [0.893 2.116]
 *     $ ./runjava  algs51.Quick3string
 *       256000 [0.235 0.739]
 *       512000 [0.404 1.719]
 *      1024000 [0.883 2.186]
 *     $ ./runjava  algs51.Quick3string
 *       256000 [0.265 0.828]
 *       512000 [0.413 1.558]
 *      1024000 [0.886 2.145]
 *
 * RESULTS WITH Arrays.sort (Mergesort)
 *
 *     $ ./runjava algs51.Quick3string
 *     dickens: [6.855]
 *     $ ./runjava algs51.Quick3string
 *     dickens: [3.650]
 *     $ ./runjava algs51.Quick3string
 *     dickens: [4.384]
 *
 * RESULTS with Quick3string (with less implemented using charAt)
 *
 *     $ ./runjava algs51.Quick3string
 *     dickens: [2.103]
 *     $ ./runjava algs51.Quick3string
 *     dickens: [2.309]
 *     $ ./runjava algs51.Quick3string
 *     dickens: [2.136]
 *
 * RESULTS with Quick3string (with less implemented using substring)
 *
 *     $ ./runjava algs51.Quick3string
 *     dickens: [6.783]
 *     $ ./runjava algs51.Quick3string
 *     dickens: [7.296]
 *     $ ./runjava algs51.Quick3string
 *     dickens: [6.995]
 *
 ***********************************************************************************/

public class Quick3string {
  private static final int CUTOFF =  15;   // cutoff to insertion sort

  // sort the array a[] of strings
  public static void sort(String[] a) {
    // StdRandom.shuffle(a);
    sort(a, 0, a.length-1, 0);
    assert isSorted(a);
  }

  // return the dth character of s, -1 if d = length of s
  private static int charAt(String s, int d) {
    assert d >= 0 && d <= s.length();
    if (d == s.length()) return -1;
    return s.charAt(d);
  }


  // 3-way string quicksort a[lo..hi] starting at dth character
  private static void sort(String[] a, int lo, int hi, int d) {

    // cutoff to insertion sort for small subarrays
    if (hi <= lo + CUTOFF) {
      insertion(a, lo, hi, d);
      return;
    }

    int lt = lo, gt = hi;
    int v = charAt(a[lo], d);
    int i = lo + 1;
    while (i <= gt) {
      int t = charAt(a[i], d);
      if      (t < v) exch(a, lt++, i++);
      else if (t > v) exch(a, i, gt--);
      else              i++;
    }

    // a[lo..lt-1] < v = a[lt..gt] < a[gt+1..hi].
    sort(a, lo, lt-1, d);
    if (v >= 0) sort(a, lt, gt, d+1);
    sort(a, gt+1, hi, d);
  }

  // sort from a[lo] to a[hi], starting at the dth character
  private static void insertion(String[] a, int lo, int hi, int d) {
    for (int i = lo; i <= hi; i++)
      for (int j = i; j > lo && less(a[j], a[j-1], d); j--)
        exch(a, j, j-1);
  }

  // exchange a[i] and a[j]
  private static void exch(String[] a, int i, int j) {
    String temp = a[i];
    a[i] = a[j];
    a[j] = temp;
  }

  // is v less than w, starting at character d
  private static boolean less1(String v, String w, int d) {
    assert v.substring(0, d).equals(w.substring(0, d));
    return v.substring(d).compareTo(w.substring(d)) < 0;
  }

  // is v less than w, starting at character d
  private static boolean less(String v, String w, int d) {
    assert v.substring(0, d).equals(w.substring(0, d));
    int len1 = v.length ();
    int len2 = w.length ();
    int n = Math.min(len1, len2);
    int k = 0;
    while (k < n) {
      char c1 = v.charAt (k);
      char c2 = w.charAt (k);
      if (c1 != c2)
        return c1 < c2;
      k++;
    }
    return len1 < len2;
  }


  // is the array sorted
  private static boolean isSorted(String[] a) {
    for (int i = 1; i < a.length; i++)
      if (a[i].compareTo(a[i-1]) < 0) return false;
    return true;
  }


  /* *********************************************************************************
   *  Test code
   ***********************************************************************************/
  private static final int MAX_LENGTH = 64;
  private static final String CHARACTERS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789`~!@#$%^&*()_-+={[}]\\|:;'\"<>,./?";
  private static String randomString() {
    int length = 2 + StdRandom.uniform (MAX_LENGTH);
    char[] text = new char[length];
    int NUM_CHARACTERS = CHARACTERS.length ();
    for (int i = 0; i < length; i++) {
      text[i] = CHARACTERS.charAt(StdRandom.uniform (NUM_CHARACTERS));
    }
    return new String(text);
  }
  private static void exch(int[] a, int i, int j) {
    int swap = a[i];
    a[i] = a[j];
    a[j] = swap;
  }
  private static double time;
  private static void countops (int N) {
    String[] a = new String[N];
    for (int i = 0; i < a.length; i++) a[i] = randomString ();
    //Arrays.sort (a);
    //Arrays.sort (a); for (int i = 0; i < (N-1)/2; i++) exch(a, i, N-i-1);

    Stopwatch sw = new Stopwatch ();
    sort (a);
    //Arrays.sort (a);
    time = sw.elapsedTime ();
  }
  public static void main(String[] args) {
    int N = 128000;
    countops (N);
    //System.exit (0);
    double prevTime = time;
    for (int i=0; i<3; i++) {
      N *= 2;
      countops (N);
      StdOut.format("%8d [%5.3f %5.3f]\n", N, time, time/prevTime);
      prevTime = time;
    }
  }
  public static void main1(String[] args) {
    String[] a = new In("data/dickens.txt").readAllStrings ();
    Stopwatch sw = new Stopwatch ();
    sort (a);
    //Arrays.sort (a);
    StdOut.format("dickens: [%5.3f]\n", sw.elapsedTime ());
  }
  public static void main2(String[] args) {
    // read in the strings from standard input
    String[] a = StdIn.readAllStrings();
    int N = a.length;

    // sort the strings
    sort(a);

    // print the results
    for (int i = 0; i < N; i++)
      StdOut.println(a[i]);
  }
}