edu.princeton.cs.algorithms.Insertion Maven / Gradle / Ivy
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package edu.princeton.cs.algorithms;
/*************************************************************************
* Compilation: javac Insertion.java
* Execution: java Insertion < input.txt
* Dependencies: StdOut.java StdIn.java
* Data files: http://algs4.cs.princeton.edu/21sort/tiny.txt
* http://algs4.cs.princeton.edu/21sort/words3.txt
*
* Sorts a sequence of strings from standard input using insertion sort.
*
* % more tiny.txt
* S O R T E X A M P L E
*
* % java Insertion < 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 Insertion < words3.txt
* all bad bed bug dad ... yes yet zoo [ one string per line ]
*
*************************************************************************/
import java.util.Comparator;
import edu.princeton.cs.introcs.StdIn;
import edu.princeton.cs.introcs.StdOut;
/**
* The Insertion class provides static methods for sorting an
* array using insertion sort.
*
* For additional documentation, see Section 2.1 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Insertion {
// This class should not be instantiated.
private Insertion() { }
/**
* Rearranges the array in ascending order, using the natural order.
* @param a the array to be sorted
*/
public static void sort(Comparable[] a) {
int N = a.length;
for (int i = 0; i < N; i++) {
for (int j = i; j > 0 && less(a[j], a[j-1]); j--) {
exch(a, j, j-1);
}
assert isSorted(a, 0, i);
}
assert isSorted(a);
}
/**
* Rearranges the array in ascending order, using a comparator.
* @param a the array
* @param c the comparator specifying the order
*/
public static void sort(Object[] a, Comparator c) {
int N = a.length;
for (int i = 0; i < N; i++) {
for (int j = i; j > 0 && less(c, a[j], a[j-1]); j--) {
exch(a, j, j-1);
}
assert isSorted(a, c, 0, i);
}
assert isSorted(a, c);
}
// return a permutation that gives the elements in a[] in ascending order
// do not change the original array a[]
/**
* Returns a permutation that gives the elements in the array in ascending order.
* @param a the array
* @return a permutation p[] such that a[p[0]], a[p[1]],
* ..., a[p[N-1]] are in ascending order
*/
public static int[] indexSort(Comparable[] a) {
int N = a.length;
int[] index = new int[N];
for (int i = 0; i < N; i++)
index[i] = i;
for (int i = 0; i < N; i++)
for (int j = i; j > 0 && less(a[index[j]], a[index[j-1]]); j--)
exch(index, j, j-1);
return index;
}
/***********************************************************************
* Helper sorting functions
***********************************************************************/
// is v < w ?
private static boolean less(Comparable v, Comparable w) {
return (v.compareTo(w) < 0);
}
// is v < w ?
private static boolean less(Comparator c, Object v, Object w) {
return (c.compare(v, 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;
}
// exchange a[i] and a[j] (for indirect sort)
private static void exch(int[] a, int i, int j) {
int 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);
}
// is the array sorted from a[lo] to a[hi]
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;
}
private static boolean isSorted(Object[] a, Comparator c) {
return isSorted(a, c, 0, a.length - 1);
}
// is the array sorted from a[lo] to a[hi]
private static boolean isSorted(Object[] a, Comparator c, int lo, int hi) {
for (int i = lo + 1; i <= hi; i++)
if (less(c, 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]);
}
}
/**
* Reads in a sequence of strings from standard input; insertion sorts them;
* and prints them to standard output in ascending order.
*/
public static void main(String[] args) {
String[] a = StdIn.readAllStrings();
Insertion.sort(a);
show(a);
}
}