Wiggle Sort Leetcode Problem 280 [Python Solution]

With Wiggle Sort, given an unsorted array of numbers, you need to reorder it in-place so that a set of predefined condition holds.

Problem Overview

The Wiggle Sort problem can be summarized as follows: Given an unsorted array of numbers, you need to reorder it in-place so that the following condition holds:

nums[0] <= nums[1] >= nums[2] <= nums[3]....

This problem can have multiple valid solutions as long as you maintain this “wiggle” pattern.

The challenge here is to achieve this reordering without creating additional arrays.

Let’s break it down step by step.

Example 1:

Input:

[3, 5, 2, 1, 6, 4]

Output:

[1, 6, 2, 5, 3, 4]

Explanation: There can be multiple valid solutions, like [2, 6, 1, 5, 3, 4].

Example 2:

Input:

[1, 2, 3, 4]

Output:

[1, 4, 2, 3]

Now, let’s explore the efficient Python solution to this problem.

Efficient Python Code Solution

def wiggleSort(self, nums):
    for i in range(1, len(nums)):
        if (i % 2 == 1 and nums[i] < nums[i - 1]) or (i % 2 == 0 and nums[i] > nums[i - 1]):
            nums[i], nums[i - 1] = nums[i - 1], nums[i]

This Python code offers an efficient way to solve the Wiggle Sort problem.

Here’s how it works:

1. We iterate through the array, starting from the second element (index 1) because there’s no previous element for the first one.
2. We check whether the current index i is odd or even.

If it’s odd, we ensure that nums[i] is greater than or equal to nums[i-1.

If it’s even, we ensure that nums[i] is less than or equal to nums[i-1].

3. If the condition is not met, we swap the elements nums[i] and nums[i-1] to correct the order.

This simple yet effective approach guarantees that the “wiggle” condition is satisfied.

The time complexity is O(n), and the space complexity is O(1), making it a highly efficient solution.

Reasoning Behind Our Approach

The reasoning behind this approach lies in the alternation pattern.

To achieve a “wiggle” sort, we need to ensure that values at odd indices are greater than or equal to the previous value, and values at even indices are less than or equal to the previous value.

By iteratively swapping values that don’t meet these conditions, we eventually obtain a valid “wiggle” sort.

And the best part is that there are multiple valid solutions for this problem.

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Conclusion

In this coding adventure, we tackled the Wiggle Sort problem, specifically LeetCode Problem 280. We used an efficient Python solution that rearranges an unsorted array in-place to satisfy the “wiggle” condition.

The alternating order of values at odd and even indices is the key to solving this problem.

We hope this walkthrough has been helpful for you.

If you have any questions, suggestions, or ideas for future coding adventures, please don’t hesitate to share them in the comments below.

Your feedback is greatly appreciated!

Happy coding! 🚀

Question Link: LintCode Problem 508