package edu.princeton.cs.algs4.ch55;
import edu.princeton.cs.introcs.*;
/***********************************************************************************
* Compilation: javac LSD.java
* Execution: java LSD < input.txt
*
* LSD radix sort
*
* - Sort a String[] array of N extended ASCII strings (R = 256), each of length W.
*
* - Sort an int[] array of N 32-bit integers, treating each integer as
* a sequence of W = 4 bytes (R = 256).
*
* Uses extra space proportional to N + R.
*
*
* % java LSD < words3.txt
* all
* bad
* bed
* bug
* dad
* ...
* yes
* yet
* zoo
*
***********************************************************************************/
public class LSD {
private final static int BITS_PER_BYTE = 8;
// LSD radix sort
public static void sort(String[] a, int W) {
int N = a.length;
int R = 256; // extend ASCII alphabet size
String[] aux = new String[N];
for (int d = W-1; d >= 0; d--) {
// sort by key-indexed counting on dth character
// compute frequency counts
int[] count = new int[R+1];
for (int i = 0; i < N; i++)
count[a[i].charAt(d) + 1]++;
// compute cumulates
for (int r = 0; r < R; r++)
count[r+1] += count[r];
// move data
for (int i = 0; i < N; i++)
aux[count[a[i].charAt(d)]++] = a[i];
// copy back
for (int i = 0; i < N; i++)
a[i] = aux[i];
}
}
// LSD sort an array of integers, treating each int as 4 bytes
// assumes integers are nonnegative
// [ 2-3x faster than Arrays.sort() ]
public static void sort(int[] a) {
int BITS = 32; // each int is 32 bits
int W = BITS / BITS_PER_BYTE; // each int is 4 bytes
int R = 1 << BITS_PER_BYTE; // each bytes is between 0 and 255
int MASK = R - 1; // 0xFF
int N = a.length;
int[] aux = new int[N];
for (int d = 0; d < W; d++) {
// compute frequency counts
int[] count = new int[R+1];
for (int i = 0; i < N; i++) {
int c = (a[i] >> BITS_PER_BYTE*d) & MASK;
count[c + 1]++;
}
// compute cumulates
for (int r = 0; r < R; r++)
count[r+1] += count[r];
// for most significant byte, 0x80-0xFF comes before 0x00-0x7F
if (d == W-1) {
int shift1 = count[R] - count[R/2];
int shift2 = count[R/2];
for (int r = 0; r < R/2; r++)
count[r] += shift1;
for (int r = R/2; r < R; r++)
count[r] -= shift2;
}
// move data
for (int i = 0; i < N; i++) {
int c = (a[i] >> BITS_PER_BYTE*d) & MASK;
aux[count[c]++] = a[i];
}
// copy back
for (int i = 0; i < N; i++)
a[i] = aux[i];
}
}
public static void main(String[] args) {
String[] a = StdIn.readAllStrings();
int N = a.length;
// check that strings have fixed length
int W = a[0].length();
for (int i = 0; i < N; i++)
assert a[i].length() == W : "Strings must have fixed length";
// sort the strings
sort(a, W);
// print results
for (int i = 0; i < N; i++)
StdOut.println(a[i]);
}
}
/*************************************************************************
* Copyright 2002-2012, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4-package.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4-package.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4-package.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with algs4-package.jar. If not, see http://www.gnu.org/licenses.
*************************************************************************/