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

 1 protected void sort(int[] toSort) {
 2         if (toSort.length <= 1) {
 3             return;
 4         }
 5         for (int i = 1; i < toSort.length; i++) {
 6             if (toSort[i] < toSort[i - 1]) {
 7                 int j = i;
 8                 int temp = toSort[i];
 9                 while (j > 0 && temp < toSort[j - 1]) {
10                     toSort[j] = toSort[j - 1];
11                     j--;
12                 }
13                 toSort[j] = temp;
14             }
15         }
16     }
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：

 1 package com.cnblogs.riyueshiwang.sort;
 2 
 3 import java.util.Arrays;
 4 
 5 public class InsertionSort extends abstractSort {
 6     @Override
 7     protected void sort(int[] toSort) {
 8         if (toSort.length <= 1) {
 9             return;
10         }
11         for (int i = 1; i < toSort.length; i++) {
12             if (toSort[i] < toSort[i - 1]) {
13                 int j = i;
14                 int temp = toSort[i];
15                 while (j > 0 && temp < toSort[j - 1]) {
16                     toSort[j] = toSort[j - 1];
17                     j--;
18                 }
19                 toSort[j] = temp;
20             }
21         }
22     }
23 
24     public static void main(String[] args) {
25         for (int j = 0, n = 2500; j < 3; j++, n = n * 10) {
26             System.out
27                     .println("**************************************************");
28             System.out.println("Number to Sort is:" + n);
29             int[] array = CommonUtils.getRandomIntArray(n, 1000000);
30             System.out.print("Array to sort is:");
31             CommonUtils.printIntArray(array);
32 
33             int[] array1 = Arrays.copyOf(array, n);
34             new InsertionSort().sortAndprint(array1);
35         }
36     }
37 }
InsertionSort.java
 1 package com.cnblogs.riyueshiwang.sort;
 2 
 3 import java.text.MessageFormat;
 4 
 5 public abstract class abstractSort {
 6     /**
 7      * 
 8      * @param toSort
 9      *            array to sort
10      */
11     protected abstract void sort(int[] toSort);
12 
13     public void sortAndprint(int[] toSort) {
14         Long begin = System.currentTimeMillis();
15         sort(toSort);
16         Long end = System.currentTimeMillis();
17         System.out.println(MessageFormat.format(
18                 "Cost time of 【{0}】 is(milliseconds):{1}", this.getClass()
19                         .getSimpleName(), (end - begin)));
20         System.out.print(MessageFormat.format("Sort result of 【{0}】:", this
21                 .getClass().getSimpleName()));
22         CommonUtils.printIntArray(toSort);
23     }
24 
25 }
abstractSort.java
 1 package com.cnblogs.riyueshiwang.sort;
 2 
 3 import java.util.Random;
 4 
 5 public class CommonUtils {
 6     private static Random random = new Random();
 7 
 8     public static void printIntArray(int[] array) {
 9         System.out.print('{');
10 
11         int length = Math.min(array.length, 10);
12         for (int i = 0; i < length; i++) {
13             System.out.print(array[i]);
14             if (i != length - 1) {
15                 System.out.print(',');
16             } else {
17                 if (array.length > 10) {
18                     System.out.print("...");
19                 }
20                 System.out.println('}');
21             }
22         }
23     }
24 
25     public static int[] getRandomIntArray(int size, int maxValue) {
26         int[] array = new int[size];
27         for (int i = 0; i < size; i++) {
28             array[i] = random.nextInt(maxValue);
29         }
30         return array;
31     }
32 
33     public static void swap(int[] toSort, int i, int j) {
34         int temp = toSort[i];
35         toSort[i] = toSort[j];
36         toSort[j] = temp;
37     }
38 }
CommonUtils.java