Interview Cake

Array Slicing

Array slicing involves taking a subset from an array and allocating a new array with those elements.

In Java you can create a new array of the elements in myArray, from startIndex to endIndex (exclusive), like this:

Arrays.copyOfRange(myArray, startIndex, endIndex);

Careful: there's a hidden time and space cost here! It's tempting to think of slicing as just "getting elements," but in reality you are:

  1. allocating a new array
  2. copying the elements from the original array to the new array

This takes time and space, where n is the number of elements in the resulting array.

That's a bit easier to see when you save the result of the slice to a variable:

int[] tailOfArray = Arrays.copyOfRange(myArray, 1, myArray.length);

But a bit harder to see when you don't save the result of the slice to a variable:

return Arrays.copyOfRange(myArray, 1, myArray.length); // whoops, I just spent O(n) time and space!
for (int item : Arrays.copyOfRange(myArray, 1, myArray.length)) { // whoops, I just spent O(n) time and space! }

So keep an eye out. Slice wisely.

See also:

What's next?

If you're ready to start applying these concepts to some problems, check out our mock coding interview questions.

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