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

一、介绍

1.时间和空间复杂度

运行过程

2.特点：

(1)对于已排序或接近排好的数据，速度很快

(2)对于部分排好序的输入，速度快

二、代码

 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[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(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);
     }
 }