[ReverseArray] #practice

ReverseArray.groovy

class ReverseArray {
    /*
Input:   str = "a,b$c"
Output:  str = "c,b$a"
Note that $ and , are not moved anywhere.
Only subsequence "abc" is reversed

Input:   str = "Ab,c,de!$"
Output:  str = "ed,c,bA!$"
     */
    static void main(String[] args) {
        println reverse('a,b$c')
        println reverse('Ab,c,de!$')
    }

    static String reverse(String input) {
        char[] arr = input.toCharArray()
        int i = 0, j = arr.length
        if (j % 2 == 0) {
            j = j / 2
        } else {
            j = (j - 1) / 2
        }
        int k = arr.length - 1
        while (k > j) {
            if (!swappable(arr[i])) {
                i++
            }
            if (!swappable(arr[k])) {
                k--
            }
            if (swappable(arr[i]) && swappable(arr[k])) {
                Character temp = arr[k]
                arr[k] = arr[i]
                arr[i] = temp
                i++
                k--
            }
        }
        arr.toString()
    }

    static boolean swappable(Character c) {
        return c.toString() ==~ /[A-Za-z0-9]/
    }
}