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125 lines
3.4 KiB
Java
125 lines
3.4 KiB
Java
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import edu.princeton.cs.introcs.StdIn;
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import edu.princeton.cs.introcs.StdOut;
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/***********************************************************************************
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* Compilation: javac MSD.java
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* Execution: java MSD < input.txt
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*
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* Reads extended ASCII string from standard input and MSD radix sorts them.
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*
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* % java MSD < shells.txt
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* are
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* by
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* sea
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* seashells
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* seashells
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* sells
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* sells
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* she
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* she
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* shells
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* shore
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* surely
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* the
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* the
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*
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***********************************************************************************/
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public class MSD {
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private static final int R = 256; // extended ASCII alphabet size
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private static final int CUTOFF = 15; // cutoff to insertion sort
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// sort array of strings
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public static void sort(String[] a) {
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int N = a.length;
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String[] aux = new String[N];
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sort(a, 0, N-1, 0, aux);
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}
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// return dth character of s, -1 if d = length of string
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private static int charAt(String s, int d) {
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assert d >= 0 && d <= s.length();
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if (d == s.length()) return -1;
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return s.charAt(d);
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}
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// sort from a[lo] to a[hi], starting at the dth character
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private static void sort(String[] a, int lo, int hi, int d, String[] aux) {
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// cutoff to insertion sort for small subarrays
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if (hi <= lo + CUTOFF) {
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insertion(a, lo, hi, d);
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return;
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}
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// compute frequency counts
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int[] count = new int[R+2];
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for (int i = lo; i <= hi; i++) {
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int c = charAt(a[i], d);
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count[c+2]++;
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}
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// transform counts to indicies
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for (int r = 0; r < R+1; r++)
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count[r+1] += count[r];
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// distribute
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for (int i = lo; i <= hi; i++) {
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int c = charAt(a[i], d);
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aux[count[c+1]++] = a[i];
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}
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// copy back
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for (int i = lo; i <= hi; i++)
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a[i] = aux[i - lo];
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// recursively sort for each character
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for (int r = 0; r < R; r++)
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sort(a, lo + count[r], lo + count[r+1] - 1, d+1, aux);
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}
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// return dth character of s, -1 if d = length of string
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private static void insertion(String[] a, int lo, int hi, int d) {
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for (int i = lo; i <= hi; i++)
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for (int j = i; j > lo && less(a[j], a[j-1], d); j--)
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exch(a, j, j-1);
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}
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// exchange a[i] and a[j]
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private static void exch(String[] a, int i, int j) {
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String temp = a[i];
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a[i] = a[j];
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a[j] = temp;
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}
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// is v less than w, starting at character d
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// DEPRECATED BECAUSE OF SLOW SUBSTRING EXTRACTION IN JAVA 7
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// private static boolean less(String v, String w, int d) {
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// assert v.substring(0, d).equals(w.substring(0, d));
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// return v.substring(d).compareTo(w.substring(d)) < 0;
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// }
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// is v less than w, starting at character d
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private static boolean less(String v, String w, int d) {
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assert v.substring(0, d).equals(w.substring(0, d));
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for (int i = d; i < Math.min(v.length(), w.length()); i++) {
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if (v.charAt(i) < w.charAt(i)) return true;
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if (v.charAt(i) > w.charAt(i)) return false;
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}
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return v.length() < w.length();
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}
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public static void main(String[] args) {
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String[] a = StdIn.readAllStrings();
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int N = a.length;
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sort(a);
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for (int i = 0; i < N; i++)
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StdOut.println(a[i]);
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}
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}
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