Java对数组实现选择排序算法的实例详解

 
public class SelectionSort { 
  public static void main(String[] args) { 
    int len = 15; 
    int[] ary = new int[len]; 
    Random random = new Random(); 
    for (int j = 0; j < len; j++) { 
      ary[j] = random.nextInt(1000); 
    } 
    System.out.println("-------排序前------"); 
//   ary=new int[]{10,9,8,7,6,5,4,3,2,1}; //测试交换次数 
//   ary=new int[]{1,2,3,4,5,6,7,8,10,9}; //测试交换次数 
    for (int j = 0; j < ary.length; j++) { 
      System.out.print(ary[j] + " "); 
    } 
     
    selectDesc(ary); 
    selectAsc(ary); 
  } 
  /* 
   * 选择排序：降序 
   */ 
  static void selectDesc(int[] ary) { 
    int compareCount = 0;//比较次数 
    int changeCount = 0;//交换次数 
    int len = ary.length; 
    int maxValueIndex = -1; //记录一轮比较下来的最小值索引 
    for (int i = 0; i < len - 1; i++) { 
      maxValueIndex = i; //从0开始 
      for (int j = i + 1; j < len; j++) { 
        if (ary[maxValueIndex] < ary[j]) { 
          maxValueIndex = j; //记录较大的索引 
          compareCount++; 
        } 
      } 
//     System.out.println("minValueIndex==" + maxValueIndex); 
      if (maxValueIndex != i) {//如果跟左边的记录索引不同，则交换 
        ary[i] = ary[maxValueIndex] + (ary[maxValueIndex] = ary[i]) * 0;//一步交换 
        changeCount++; 
      } 
    } 
     
    System.out.println("\n-------降序排序后------比较次数：" + compareCount + "，交换次数" + changeCount); 
    for (int j = 0; j < ary.length; j++) { 
      System.out.print(ary[j] + " "); 
    } 
  } 
   
  /* 
   * 选择排序：升序 
   */ 
  static void selectAsc(int[] ary) { 
    int compareCount = 0, changeCount = 0; 
    int len = ary.length; 
    int minIndex = -1; 
    for (int i = 0; i < len - 1; i++) { 
      minIndex = i; 
      for (int j = i + 1; j < len; j++) { 
        if (ary[minIndex] > ary[j]) { 
          minIndex = j; //记录较小的索引 
          compareCount++; 
        } 
      } 
      if (minIndex != i) {//如果跟左边的记录索引不同，则交换 
        ary[i] = ary[minIndex] + (ary[minIndex] = ary[i]) * 0; 
        changeCount++; 
      } 
    } 
    System.out.println("\n-------升序排序后------比较次数：" + compareCount + "，交换次数" + changeCount); 
    for (int j = 0; j < ary.length; j++) { 
      System.out.print(ary[j] + " "); 
    } 
  } 
} 

-------排序前------ 
125 350 648 789 319 699 855 755 552 489 187 916 596 731 852  
-------降序排序后------比较次数：26，交换次数13 
916 855 852 789 755 731 699 648 596 552 489 350 319 187 125  
-------升序排序后------比较次数：56，交换次数7 
125 187 319 350 489 552 596 648 699 731 755 789 852 855 916