Introduction

In this blog post, we will explore how to solve the LeetCode problem "376" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

A wiggle sequence is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with one element and a sequence with two non-equal elements are trivially wiggle sequences. For example, [1, 7, 4, 9, 2, 5] is a wiggle sequence because the differences (6, -3, 5, -7, 3) alternate between positive and negative. In contrast, [1, 4, 7, 2, 5] and [1, 7, 4, 5, 5] are not wiggle sequences. The first is not because its first two differences are positive, and the second is not because its last difference is zero. A subsequence is obtained by deleting some elements (possibly zero) from the original sequence, leaving the remaining elements in their original order. Given an integer array nums, return the length of the longest wiggle subsequence of nums. Example 1: Input: nums = [1,7,4,9,2,5] Output: 6 Explanation: The entire sequence is a wiggle sequence with differences (6, -3, 5, -7, 3). Example 2: Input: nums = [1,17,5,10,13,15,10,5,16,8] Output: 7 Explanation: There are several subsequences that achieve this length. One is [1, 17, 10, 13, 10, 16, 8] with differences (16, -7, 3, -3, 6, -8). Example 3: Input: nums = [1,2,3,4,5,6,7,8,9] Output: 2 Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 1000 Follow up: Could you solve this in O(n) time?

Explanation

Here's the breakdown of the solution and the code:

• High-level approach:

  • Use dynamic programming to track the longest wiggle subsequence ending at each index, considering two states: "up" (last difference was positive) and "down" (last difference was negative).
  • Iterate through the array, updating the "up" and "down" states based on whether the current element creates an increasing or decreasing difference with the previous element.
  • The final result is the maximum of the last "up" and "down" values.

• Complexity:

  • Runtime Complexity: O(n)
  • Storage Complexity: O(1)

Code

    def wiggleMaxLength(nums):
    """
    Finds the length of the longest wiggle subsequence of nums.

    Args:
        nums: An integer array.

    Returns:
        The length of the longest wiggle subsequence.
    """

    if not nums:
        return 0

    up = 1
    down = 1

    for i in range(1, len(nums)):
        if nums[i] > nums[i - 1]:
            up = down + 1
        elif nums[i] < nums[i - 1]:
            down = up + 1

    return max(up, down)