选择排序（selection sort）

选择排序也是最基本的排序算法之一，其算法复杂度为O(n^2)，与待排序数组的内部结构没有关系。

算法简介

选择排序，顾名思义就是通过选择来排序。从一堆数中选出最小的放在第一位，在剩下的数中在选择最小的排在第二位。。。选择，就是一个比较的过程，从一堆数据中选择就是要在这个数据堆中一个一个进行比较。算法外层循环执行n次，每次一定进行i次比较操作，所以算法复杂度为n^2。非常直观的算法。

代码

package sorting;public class Data {/** * generate an unsorted array of length n * @param n length * @param max the maximum integer element of this array * @return an unsorted array consists of elements range from 1 to max */public static int[] getArray(int n, int max){int[] result = new int[n];for(int i =0; i < n; i++){result[i] = (int)(Math.random() * max + 1);}return result;}/** * print the array * @param arg array */public static void printArray(int[] arg){StringBuffer temp = new StringBuffer();for(int i = 0; i < arg.length; i++){temp.append(arg[i] + "\t");}System.out.println(temp);}}

package sorting;public class SelectionSort {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubSelectionSort ss = new SelectionSort();int[] data = Data.getArray(10, 100);System.out.print("Source data:\t");Data.printArray(data);ss.selectionSort(data);System.out.print("Sorted data:\t");Data.printArray(data);}public void selectionSort(int[] arg){int index = 0, min = 0, j = 0;// why i < length -1?// because when i equals length - 1, the rest of the array contains only 1 number.// after this time of loop, arg[arg.length - 1]must be the minimum one// in order to promote efficiency, wo should assign arg.length -  1 to a constant,// and use this constant in the compare statement for(int i = 0; i < arg.length - 1; i++){index = i; min = arg[i];// find the minimal number in the rest of the arrayfor(j = i + 1; j < arg.length; j++){if(arg[j] < min){index = j;min = arg[j];}}//need switchif(index != i){arg[index] = arg[i];arg[i] = min;}}}}