排序算法一：插入排序(Insertion sort)

最近从网易公开课在看麻省理工学院的公开课《算法导论》，感觉还不错，接下来几篇文章所示学习日记了，不准备对算法细节做过多描述，感兴趣的可以自己去看。

文章分几篇讲经典排序算法，直接上代码，根据结果对算法性能有个直观了解。本篇先说插入排序（insertion sort）。

(一)算法实现

 protected void sort(int[] toSort) {
         if (toSort.length <= 1) {
             return;
         }
         for (int i = 1; i < toSort.length; i++) {
             if (toSort[i] < toSort[i - 1]) {
                 int j = i;
                 int temp = toSort[i];
                 while (j > 0 && temp < toSort[j - 1]) {
                     toSort[j] = toSort[j - 1];
                     j--;
                 }
                 toSort[j] = temp;
             }
         }
     }

Insertion sort

1）插入排序属于原地排序，节省空间

2）插入排序的时间复杂度是O(n²)

3）插入排序属于比较排序

4）插入排序属于稳定排序算法

（二）算法性能

**************************************************
Number to Sort is:2500
Array to sort is:{665184,192100,475135,171530,869545,506246,640618,543738,91353,493005...}
Cost time of 【InsertionSort】 is(milliseconds):3
Sort result of 【InsertionSort】:{856,985,2432,3792,3910,3915,4423,4516,4653,4780...}
**************************************************
Number to Sort is:25000
Array to sort is:{99880,631403,265087,597224,876665,955084,996547,879081,197806,926881...}
Cost time of 【InsertionSort】 is(milliseconds):267
Sort result of 【InsertionSort】:{14,14,17,83,97,152,179,199,240,299...}
**************************************************
Number to Sort is:250000
Array to sort is:{777293,731773,508229,920721,338608,707195,940,445210,19071,768830...}
Cost time of 【InsertionSort】 is(milliseconds):21,523
Sort result of 【InsertionSort】:{2,7,7,19,19,21,24,29,30,39...}

相关代码：

 package com.cnblogs.riyueshiwang.sort;

 import java.util.Arrays;

 public class InsertionSort extends abstractSort {
     @Override
     protected void sort(int[] toSort) {
         if (toSort.length <= 1) {
             return;
         }
         for (int i = 1; i < toSort.length; i++) {
             if (toSort[i] < toSort[i - 1]) {
                 int j = i;
                 int temp = toSort[i];
                 while (j > 0 && temp < toSort[j - 1]) {
                     toSort[j] = toSort[j - 1];
                     j--;
                 }
                 toSort[j] = temp;
             }
         }
     }

     public static void main(String[] args) {
         for (int j = 0, n = 2500; j < 3; j++, n = n * 10) {
             System.out
                     .println("**************************************************");
             System.out.println("Number to Sort is:" + n);
             int[] array = CommonUtils.getRandomIntArray(n, 1000000);
             System.out.print("Array to sort is:");
             CommonUtils.printIntArray(array);

             int[] array1 = Arrays.copyOf(array, n);
             new InsertionSort().sortAndprint(array1);
         }
     }
 }

InsertionSort.java

 package com.cnblogs.riyueshiwang.sort;

 import java.text.MessageFormat;

 public abstract class abstractSort {
     /**
      *
      * @param toSort
      *            array to sort
      */
     protected abstract void sort(int[] toSort);

     public void sortAndprint(int[] toSort) {
         Long begin = System.currentTimeMillis();
         sort(toSort);
         Long end = System.currentTimeMillis();
         System.out.println(MessageFormat.format(
                 "Cost time of 【{0}】 is(milliseconds):{1}", this.getClass()
                         .getSimpleName(), (end - begin)));
         System.out.print(MessageFormat.format("Sort result of 【{0}】:", this
                 .getClass().getSimpleName()));
         CommonUtils.printIntArray(toSort);
     }

 }

abstractSort.java

 package com.cnblogs.riyueshiwang.sort;

 import java.util.Random;

 public class CommonUtils {
     private static Random random = new Random();

     public static void printIntArray(int[] array) {
         System.out.print('{');

         int length = Math.min(array.length, 10);
         for (int i = 0; i < length; i++) {
             System.out.print(array[i]);
             if (i != length - 1) {
                 System.out.print(',');
             } else {
                 if (array.length > 10) {
                     System.out.print("...");
                 }
                 System.out.println('}');
             }
         }
     }

     public static int[] getRandomIntArray(int size, int maxValue) {
         int[] array = new int[size];
         for (int i = 0; i < size; i++) {
             array[i] = random.nextInt(maxValue);
         }
         return array;
     }

     public static void swap(int[] toSort, int i, int j) {
         int temp = toSort[i];
         toSort[i] = toSort[j];
         toSort[j] = temp;
     }
 }

CommonUtils.java