Rotating arrays in java

In summary, the code provided is meant to rotate an array 90 degrees to the left, but it appears to be doing something else. It takes in an array of dimensions M x N and outputs an array of the same dimensions, which is not what one would expect from a rotation. Additionally, the line of code given is confusing as it uses i three times and k only once, making it unclear what it is actually doing. It would be helpful to provide more context and information on what the code is meant to do.
  • #1
physicsfun
11
0
I am supposed to write code to rotate an array 90 degrees to the left... so my question is, why is this code not rotating my array 90 degrees to the left?

thanks for any help!



public static int[][] rotateLeft(int[][] source) {
int[][] result = new int[source.length][source[0].length];
for (int i = 0; i < result.length; i++) {
for (int k = 0; k < result[0].length; k++) {
result[k] = source[source.length-1-i];}}
return result;}
 
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  • #2
It would be helpful if you would tell us what your code turns out to be doing instead of rotating the array 90 degrees to the left.

However, this said:

1. You take in an array of dimensions M x N, and put out an array of dimensions M x N. If it was rotated wouldn't it be N x M?

2. Just look at this line of code:

result[k] = source[source.length-1-i];

What does this do? Why does i appear three times and k just one?
 
  • #3



There could be several reasons why the code is not rotating the array 90 degrees to the left. Here are some potential issues to consider:

1. The code may not be properly accessing and assigning values to the elements of the array. Make sure that the indices used in the for loops are correct and that the correct elements are being accessed and assigned.

2. The code may not be rotating the array in the desired direction. In the code provided, the array is being rotated to the left, but if the desired rotation is to the right, the code would need to be modified accordingly.

3. The code may not be handling edge cases properly. For example, if the array is not a perfect square, the rotation algorithm may need to be adjusted to account for the differing dimensions.

4. There may be errors or bugs in the code that are preventing the rotation from occurring correctly. It may be helpful to debug the code or use a different approach to rotating the array.

It's also important to make sure that the input array is being passed correctly to the rotateLeft() function and that the output array is being used correctly after the function returns. Overall, it may be helpful to thoroughly review the code and consider these potential issues to determine why the rotation is not occurring as expected.
 

1. How do you rotate arrays in Java?

In Java, you can rotate an array using the System.arraycopy() method. This method takes in the original array, the starting index, and the destination array as parameters. It then copies the elements from the original array to the destination array starting from the given index. Once the elements are copied, you can use a for loop to add the remaining elements from the original array to the end of the destination array.

2. Can you rotate an array in-place in Java?

Yes, you can rotate an array in-place in Java. This means that the rotation is done without creating a new array. To achieve this, you can use a temporary variable to store the first element of the array, then shift all the elements of the array to the left by one position. Finally, assign the first element to the last position of the array. This process can be repeated for the desired number of rotations.

3. How do you rotate arrays in Java using collections?

If you are using the java.util.Collections library, you can use the Collections.rotate() method to rotate an array. This method takes in the array and the number of positions to rotate as parameters. It automatically handles the rotation and returns the rotated array. However, please note that this method creates a new array, so it might not be the most efficient solution for large arrays.

4. How do you rotate a 2D array in Java?

In order to rotate a 2D array in Java, you can use the same logic as rotating a 1D array. First, you rotate the outermost layer of the array, then the next layer, and so on until you reach the center of the array. This can be achieved using nested for loops and temporary variables. Alternatively, you can use the java.util.Arrays library and its Arrays.deepToString() method to convert the 2D array into a string and then rotate the string using the techniques mentioned earlier.

5. What is the time complexity of rotating arrays in Java?

The time complexity of rotating an array in Java depends on the method used. If you are using System.arraycopy() or performing the rotation in-place, the time complexity is O(n), where n is the number of elements in the array. However, if you are using the Collections.rotate() method, the time complexity is O(n^2), as it involves creating a new array each time the method is called.

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