一堆Sort的Java代码实现

把一些Java实现的Sort整合一下,不过还缺少TimSort, HeapSort 这些,python 默认的Sort 是使用的TimSort.
第一个Selection Sort 是自己写的，和后面的Selection Sort不同在于，这个版本多了个swap方法来交换两个element.
并且这个版本是外层循环每次都找到一个最小的，放在数组最前面。

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1. package Algorithms;
   
2. 
   
3. public class SelectionSort {
   
4. 
   
5.     private static void swap(int indexA, int indexB, int[] arr){
   
6.         int temp;
   
7.         temp=arr[indexA];
   
8.         arr[indexA]=arr[indexB];
   
9.         arr[indexB]=temp;
   
10.     }
    
11. 
    
12.     public static void selectionSort(int arr[]){
    
13.         int minIndex;
    
14.         for(int i=0;i<=arr.length-2;i++){
    
15.             minIndex=i;
    
16.             for(int j=i+1;j<=arr.length-1;j++){
    
17.                 if(arr[minIndex] > arr[j]){
    
18.                     minIndex=j;
    
19.                 }
    
20.             }
    
21.             swap( i, minIndex, arr);
    
22.         }
    
23.     }
    
24. 
    
25.     public static void main(String[] args) {
    
26.         int arr[]= new int[]{5,3,1,10, 7,6, 12, 0};
    
27.         selectionSort(arr);
    
28.         for(int i: arr){
    
29.             System.out.print(i+" ");
    
30.         }
    
31.     }
    
32. }

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1. package Sort;
   
2. 
   
3. import java.util.Arrays;
   
4. import java.util.Random;
   
5. 
   
6. public class ArraySort {
   
7.     public static void SelectionSort(int[] arr){
   
8.         int index;
   
9.         for(int i=1;i<arr.length;i++){
   
10.             index=0;
    
11.             for(int j=1;j<=arr.length-i;j++){
    
12.                 if(arr[j] > arr[index]){
    
13.                     index=j;        //find max assign to index
    
14.                 }
    
15.             }
    
16.             //swap arr.length-i and index (max)
    
17.             int temp=arr[arr.length-i];
    
18.             arr[arr.length-i]=arr[index];
    
19.             arr[index]=temp;
    
20.         }
    
21.     }
    
22.     
    
23.     public static void insertSort(int[] arr){
    
24.         for(int i=1;i<arr.length;i++){
    
25.             int key=arr[i];
    
26.             int j = i-1;
    
27.             while(j>=0 && key < arr[j]){
    
28.                 arr[j+1]=arr[j];
    
29.                 j--;
    
30.             }
    
31.             arr[j+1]=key;
    
32.         }
    
33.     }
    
34.     
    
35.     public static void BubbleSort(int[] arr){
    
36.         for(int i=1;i<arr.length;i++){
    
37.             //比较相邻两个元素,较大的往后冒泡
    
38.             for(int j=0;j<arr.length-i;j++){
    
39.                 if(arr[j] > arr[j+1]){
    
40.                     int temp=arr[j];
    
41.                     arr[j]=arr[j+1];
    
42.                     arr[j+1]=temp;
    
43.                 }
    
44.             }
    
45.         }
    
46.     }
    
47.             
    
48.     public static void quickSort(int arr[],int lowIndex,int highIndex){
    
49.         int lo=lowIndex;
    
50.         int hi=highIndex;
    
51.         int mid;
    
52.         if(highIndex > lowIndex){
    
53.             mid=arr[(lowIndex+highIndex)/2];    //pivot
    
54.             while(lo <= hi){
    
55.                 while((lo<highIndex) && (arr[lo] < mid))
    
56.                     ++lo;
    
57.                 while((hi>lowIndex) && (arr[hi]> mid))
    
58.                     --hi;
    
59.                 if(lo <= hi){
    
60.                     swap(arr,lo,hi);
    
61.                     ++lo;
    
62.                     --hi;
    
63.                 }
    
64.             }
    
65.             if(lowIndex < hi)
    
66.                 quickSort(arr, lowIndex, hi);
    
67.             if(lo < highIndex)
    
68.                 quickSort(arr, lo, highIndex);
    
69.         }
    
70.         
    
71.     }
    
72.     
    
73.     private static void swap(int arr[] ,int i, int j){
    
74.         int temp= arr[i];
    
75.         arr[i]=arr[j];
    
76.         arr[j]=temp;
    
77.     }
    
78.     
    
79.     
    
80.     public static void randomFill(int[] data,int max){
    
81.         Random gen = new Random();
    
82.         for(int i=0;i<data.length;i++){
    
83.             data[i]=gen.nextInt(max);
    
84.         }
    
85.     }
86. 
    
87.     public static void main(String[] args){
    
88.         int[] data = new int[10];
    
89.         randomFill(data , 1000);
    
90.         System.out.println(Arrays.toString(data));
    
91.         System.out.println("after sort");
    
92.         //insertSort(data);
    
93.         //SelectionSort(data);
    
94.         //bubbleSort(data);
    
95.         quickSort(data,0, data.length-1);
    
96.         System.out.println(Arrays.toString(data));
    
97.     }
    
98. }

2. 最近看到个有趣的题目, 传入一个String 看看是否能转化为Numeric .
http://rosettacode.org/wiki/Determine_if_a_string_is_numeric#Java
这里有很多的代码实现,我测试下了Java的一些实现.

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1. package hezhb_test;
   
2. 
   
3. import java.text.NumberFormat;
   
4. import java.text.ParsePosition;
   
5. import java.util.Scanner;
   
6. 
   
7. public class IsNumeric {
   
8. //Determine a String is a Numeric or not
   
9.         
   
10.     public static boolean isNumeric(String inputData) {
    
11.         return inputData.matches("[-+]?\\d+(\\.\\d+)?");
    
12.     }
    
13.         
    
14.     public static boolean isNumeric2(String inputData) {
    
15.         if (inputData.equals("")){
    
16.             return false;
    
17.         }
    
18.         NumberFormat formatter = NumberFormat.getInstance();
    
19.         ParsePosition pos = new ParsePosition(0);
    
20.         formatter.parse(inputData, pos);
    
21.         return inputData.length() == pos.getIndex();
    
22.     }
    
23.         
    
24.     public static boolean isNumeric3(String input){
    
25.         Scanner s = new Scanner(input);
    
26.         return s.hasNextInt();
    
27.     }
    
28.         
    
29.     public static void main(String[] args) {
    
30.     // TODO Auto-generated method stub
    
31.             
    
32.         System.out.println(isNumeric("-1999.456"));
    
33.         System.out.println(isNumeric(""));
    
34.         System.out.println(isNumeric2("-1999.456"));
    
35.         System.out.println(isNumeric2(""));
    
36.         System.out.println(isNumeric3("-1999"));
    
37.         System.out.println(isNumeric3(""));
    
38.         }
    
39.     }

结果如下,isNumeric3 这个函数只能处理整数, 而isNumeric2 我在其中增加了判断是不是空的字符串,为空则直接返回false, 这个地方有待商榷,到底空字符串应该理解为数字0 ,还是不能看作为一个数字呢.
综上感觉前两个实现比较好,如果空字符串可以看作数字0,那么isNumeric2 很适用,否则用正则表达式很适用, 正则表达式的问题是太多的反斜线太难看懂了, Python的re.compile(r"") 裸字符串可以少写一个"\",
Java我还不清楚怎么写简单些.

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1. true
   
2. false
   
3. true
   
4. false
   
5. true
   
6. false

3. 贴一个linux下cal命令的Java实现.

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1. package hezhb_test;
   
2. 
   
3. import java.time.DayOfWeek;
   
4. import java.time.LocalDate;
   
5. 
   
6. //A implementation of Linux command "cal":
   
7. public class Cal {
   
8. 
   
9.     public static void main(String[] args) {
   
10.         // TODO Auto-generated method stub
    
11.         LocalDate date = LocalDate.now().withDayOfMonth(1);
    
12.         int month;
    
13.         if(args.length >= 2){
    
14.             month=Integer.parseInt(args[0]);
    
15.             int year = Integer.parseInt(args[1]);
    
16.             date=LocalDate.of(year,month,1);
    
17.         }else{
    
18.             month=date.getMonthValue();
    
19.         }
    
20.         
    
21.         System.out.println(" Mon Tue Wed Thu Fri Sat Sun");
    
22.         DayOfWeek weekday = date.getDayOfWeek();
    
23.         int value = weekday.getValue();
    
24.         for(int i=1;i<value;i++){
    
25.             System.out.print(" ");
    
26.         }
    
27.         while(date.getMonthValue() == month){
    
28.             System.out.printf("%4d", date.getDayOfMonth());
    
29.             date = date.plusDays(1);
    
30.             if(date.getDayOfWeek().getValue() ==1)
    
31.                 System.out.println();
    
32.         }
    
33.         if(date.getDayOfWeek().getValue()!= 1){
    
34.             System.out.println();
    
35.         }
    
36.     }
    
37. }