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)
（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