I've written a recursive method for reversing an array.
It produces a StackOverflowError, and I just can't figure out why. I'm sure it's something simple, but I've been stuck here for 2 hours trying to fix it.
My code:
public static void reverseArray(char[] input, int i, int j) {
char temp;
if (i >= j) return;
else if (i < j) {
temp = input[i];
input[i] = input[j];
input[j] = temp;
reverseArray(input, i++, j--);
}
}
You should change the post-increment/post-decrement to pre-increment/pre-decrement in the recursive call:
reverseArray(input, ++i, --j);
i++ would change only the value of i that exists in the scope of the current method call, but the argument received by the recursive call would be the initial value of i (same holds true for j).
So basically you're passing the same indices and for that reason getting a StackOverflowError.
Also note that there's no need to wrap the recursive case with else if.
public static void reverseArray(char[] input, int i, int j) {
if (i >= j) return;
char temp = input[i];
input[i] = input[j];
input[j] = temp;
reverseArray(input, ++i, --j);
}
Alternatively, as @Slaw has suggested in the comments, to avoid confusion you can explicitly add/subtract one while making a recursive call:
reverseArray(input, i + 1, j - 1);
++i and --j). See the online demo. I've added a print statement and removed some redundancy.
i + 1 and j - 1, just to make it completely clear.Try fixing (x++, y--) to (++x, --y)
