Solution.java

class Solution {
    
    // temp: input array
    // n: size of array
    //Function to rearrange  the array elements alternately.
    public static void rearrange(int arr[], int n){
        for (int i = 0; i < arr.length; i++) {
            int index = i;
            int next = arr[index];
            if (next < 0) continue;
            index = newIndex(index, arr.length);
            while (index != i) {
                int tmp = arr[index];
                arr[index] = -next;
                next = tmp;
                index = newIndex(index, arr.length);
            }
            arr[index] = -next;
        }
        for (int i = 0; i < arr.length; i++) {
            arr[i] = -arr[i];
        }
    }
    
    private static int newIndex(int i, int size) {
        int ordinal = i + 1;
        return ordinal > size / 2 ? 2 * (size - i - 1) : ordinal * 2 - 1; 
    }
}