Given an unsorted array nums, reorder it in-place such that nums[0] <= nums[1] >= nums[2] <= nums[3]….

For example, given nums = [3, 5, 2, 1, 6, 4], one possible answer is [1, 6, 2, 5, 3, 4].

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O(nlogn) time O(1) space sort solution

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public class Solution {
    public void wiggleSort(int[] nums) {
        Arrays.sort(nums);
        for (int i = 1; i < nums.length - 1; i += 2) {
            int temp = nums[i];
            nums[i] = nums[i + 1];
            nums[i + 1] = temp;
        }
    }
}

O(n) time O(1) space one pass solution

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public class Solution {
    public void wiggleSort(int[] nums) {
        for (int i = 0; i < nums.length - 1; i++) {
            if ((i % 2 == 0 && nums[i] > nums[i + 1]) || ((i % 2 == 1 && nums[i] < nums[i + 1]))) {
                int temp = nums[i];
                nums[i] = nums[i + 1];
                nums[i + 1] = temp;
            }
        }
    }
}
Amazing short code from here
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public class Solution {
    public void wiggleSort(int[] nums) {
        for (int i = 1; i < nums.length; i++) {
            int cur = nums[i - 1];
            if ((i % 2 == 1) == (cur > nums[i])) {
                nums[i - 1] = nums[i];
                nums[i] = cur;
            }
        }
    }
}