将数组元素左移到java中

Question

我正在编写java中的SDES密码，正在将两个长度为5的数组向左移动一个空间，这对于p10kleft变为shiftp10kleft变得很好，但是当我将相同的代码应用于p10kright以成为shiftp10kright，它将在末尾添加一个随机1而不是将第一个0移到最后一位。

该处是我的代码：

package ciphers; 
import java.io.*; 
import java.lang.reflect.Array; 
import java.util.Arrays; 
import java.util.Collections; 

public class SDESNew { 

    public static void main(String []arg)throws Exception 
    { 
     int[] k = {1,1,1,1,0,1,1,0,0,0}; 
     int[] P10 = {3,5,2,7,4,10,1,9,8,6}; 
     int[] P8 = {6,3,7,4,8,5,10,9}; 
     int[] P4 = {2,4,3,1}; 
     int[] IP = {2,6,3,1,4,8,5,7}; 
     int[] EP = {4,1,2,3,2,3,4,1}; 
     int S0[][] = { 
         {1,0,3,2}, 
         {3,2,1,0}, 
         {0,2,1,3}, 
         {3,1,3,2} 
        }; 

     int S1[][] = { 
         {0,1,2,3}, 
         {2,0,1,3}, 
         {3,0,1,2}, 
         {2,1,0,3} 
        }; 

     //Arrays that we have to calculate 
     int p10k[]=new int[10]; //Create p10(k) array 
     int[] p10kleft = new int[5]; 
     int[] p10kright = new int[5]; 
     int[] shiftp10kleft = new int[5]; 
     int[] shiftp10kright = new int[5]; 



     for(int i=0;i<10;i++) 
     { 
      System.out.println("Value from array P10: " +P10[i]);       //Printing values from array P10 
      System.out.println("Array position to be used in array k: "  +(P10[i]-1)); //Array position begins at 0 so subtracting 1 from P10 position so array begins at 0 
      System.out.println(k[P10[i]-1]); //Printing values in array positions 
      p10k[i]=k[P10[i]-1]; //Putting array values in p10k array 
      System.out.println(""); 
     } 
     System.out.println("P10k: " +Arrays.toString(p10k)); //Printing out all values in p10k array 

     System.arraycopy(p10k, 0, p10kleft, 0, p10kleft.length); 
     System.arraycopy(p10k, p10kleft.length, p10kright, 0, p10kright.length); 

     System.out.println("Left: " +Arrays.toString(p10kleft)); 
     System.out.println("Right: " +Arrays.toString(p10kright)); 



     // System.arraycopy(p10kleft, 1, shiftp10kleft, 0, p10kleft.length - 1); 

     int n = p10kleft.length; 
     shiftp10kleft = p10kleft; 
     int i = 0; 
     if (n>0) 
     { 
      for(i=0; i<n-1; i++) 
      { 
       p10kleft[i]=p10kleft[i+1]; 
      } 
     } 
     p10kleft[i] = shiftp10kleft[i]; 


     System.out.println("Shift Left: " +Arrays.toString(shiftp10kleft)); 




     n = p10kright.length; 
     shiftp10kright = p10kright; 
     i = 0; 
     if (n>0) 
     { 
      for(i=0; i<n-1; i++) 
      { 
       p10kright[i]=p10kright[i+1]; 
      } 
     } 
     p10kright[i] = shiftp10kright[i]; 


     System.out.println("Shift Right: " +Arrays.toString(shiftp10kright)); 


     } 

     } 

这里是电流输出：

Value from array P10: 3 
Array position to be used in array k: 2 
1 

Value from array P10: 5 
Array position to be used in array k: 4 
0 

Value from array P10: 2 
Array position to be used in array k: 1 
1 

Value from array P10: 7 
Array position to be used in array k: 6 
1 

Value from array P10: 4 
Array position to be used in array k: 3 
1 

Value from array P10: 10 
Array position to be used in array k: 9 
0 

Value from array P10: 1 
Array position to be used in array k: 0 
1 

Value from array P10: 9 
Array position to be used in array k: 8 
0 

Value from array P10: 8 
Array position to be used in array k: 7 
0 

Value from array P10: 6 
Array position to be used in array k: 5 
1 

P10k: [1, 0, 1, 1, 1, 0, 1, 0, 0, 1] 

Left: [1, 0, 1, 1, 1] 

Right: [0, 1, 0, 0, 1] 

Shift Left: [0, 1, 1, 1, 1] 

Shift Right: [1, 0, 0, 1, 1] 

---

我需要右移正确输出[1，0，0，1，0]

Answer 1

如在注释中那样，在进入循环之前将第一个值存储在基元中：

 int n = p10kleft.length; 
    shiftp10kleft = p10kleft; 
    int i = 0; 
    int first = p10kleft[i]; 
    if (n>0) 
    { 
     for(i=0; i<n-1; i++) 
     { 
      p10kleft[i]=p10kleft[i+1]; 
     } 
    } 
    p10kleft[i] = first; 

关于你提到的其他问题，重复此操作3次是明显的（而不是特别聪明，或者有效的方式）来做到这一点：

for(int shiftCounter = 0; shiftCounter < 3; shiftCounter++) { 
    int n = p10kleft.length; 
    ... 
    p10kleft[i] = first; 
} 

在任何情况下，有一些更好的方法正如我已经建议的那样。但是，如果你在阵列上死了，你至少可以使用System.arraycopy。一个简单的例子是：

static int[] shiftLeft(int[] arr, int shift) { 
    int[] tmp = new int[arr.length]; 
    System.arraycopy(arr, shift, tmp, 0, arr.length-shift); 
    System.arraycopy(arr, 0, tmp, arr.length-shift, shift); 
    return tmp; 
} 

，然后用它是这样的：

p10kleft = shiftLeft(p10kleft, 1); // shift once 
p10kleft = shiftLeft(p10kleft, 3); // shift 3 times 

编辑：修正参数顺序arraycopy。