算法Sedgewick第四版-第1章基础-2.1Elementary Sortss-002插入排序法(Insertion sort)

package algorithms.elementary21;

/******************************************************************************
*  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 algorithms.util.StdIn;
import algorithms.util.StdOut;

/**
*  The <tt>Insertion</tt> class provides static methods for sorting an
*  array using insertion sort.
*  <p>
*  This implementation makes ~ 1/2 N^2 compares and exchanges in
*  the worst case, so it is not suitable for sorting large arbitrary arrays.
*  More precisely, the number of exchanges is exactly equal to the number
*  of inversions. So, for example, it sorts a partially-sorted array
*  in linear time.
*  <p>
*  The sorting algorithm is stable and uses O(1) extra memory.
*  <p>
*  See <a href="http://algs4.cs.princeton.edu/21elementary/InsertionPedantic.java.html">InsertionPedantic.java</a>
*  for a version that eliminates the compiler warning.
*  <p>
*  For additional documentation, see <a href="http://algs4.cs.princeton.edu/21elementary">Section 2.1</a> of
*  <i>Algorithms, 4th Edition</i> 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 subarray a[lo..hi] in ascending order, using the natural order.
* @param a the array to be sorted
* @param lo left endpoint
* @param hi right endpoint
*/
public static void sort(Comparable[] a, int lo, int hi) {
for (int i = lo; i <= hi; i++) {
for (int j = i; j > lo && less(a[j], a[j-1]); j--) {
exch(a, j, j-1);
}
}
assert isSorted(a, lo, hi);
}

/**
* Rearranges the array in ascending order, using a comparator.
* @param a the array
* @param comparator the comparator specifying the order
*/
public static void sort(Object[] a, Comparator comparator) {
int N = a.length;
for (int i = 0; i < N; i++) {
for (int j = i; j > 0 && less(a[j], a[j-1], comparator); j--) {
exch(a, j, j-1);
}
assert isSorted(a, 0, i, comparator);
}
assert isSorted(a, comparator);
}

/**
* Rearranges the subarray a[lo..hi] in ascending order, using a comparator.
* @param a the array
* @param lo left endpoint
* @param hi right endpoint
* @param comparator the comparator specifying the order
*/
public static void sort(Object[] a, int lo, int hi, Comparator comparator) {
for (int i = lo; i <= hi; i++) {
for (int j = i; j > lo && less(a[j], a[j-1], comparator); j--) {
exch(a, j, j-1);
}
}
assert isSorted(a, lo, hi, comparator);
}

// 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 <tt>p[]</tt> such that <tt>a[p[0]]</tt>, <tt>a[p[1]]</tt>,
*    ..., <tt>a[p[N-1]]</tt> are in ascending order
*/
public static int[] indexSort(Comparable[] a) {
int N = a.length;
int[] index = new int
;
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(Object v, Object w, Comparator comparator) {
return comparator.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 comparator) {
return isSorted(a, 0, a.length - 1, comparator);
}

// is the array sorted from a[lo] to a[hi]
private static boolean isSorted(Object[] a, int lo, int hi, Comparator comparator) {
for (int i = lo + 1; i <= hi; i++)
if (less(a[i], a[i-1], comparator)) 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);
}
}