public class WiggleSort {

    /**
     * Sorts the array in-place into a wiggle pattern.
     * @param nums the array of integers to be wiggle sorted.
     */
    public static void sort(int[] nums) {
        // Defensive check to prevent NullPointerException
        if (nums == null || nums.length <= 1) {
            return; 
        }

        for (int i = 0; i < nums.length - 1; i++) {
            // If index is even, current element should be <= next element
            // If index is odd, current element should be >= next element
            if ((i % 2 == 0) ? nums[i] > nums[i + 1] : nums[i] < nums[i + 1]) {
                swap(nums, i, i + 1);
            }
        }
    }

    private static void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}