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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 }
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 }
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 }
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 }
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原文地址：http://www.cnblogs.com/riyueshiwang/p/4591136.html
