Wiggle Subsequence — LeetCode 376 Python Solution

The problem

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.

Example

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).

Python solution

class Solution:
    def wiggleMaxLength(self, nums: List[int]) -> int:
        n = len(nums)
        ans = 1
        f = [1] * n
        g = [1] * n
        for i in range(1, n):
            for j in range(i):
                if nums[j] < nums[i]:
                    f[i] = max(f[i], g[j] + 1)
                elif nums[j] > nums[i]:
                    g[i] = max(g[i], f[j] + 1)
            ans = max(ans, f[i], g[i])
        return ans

Complexity

Pattern: Greedy

Take the locally best option every time — when you can prove that never costs you later. LeetCode 376. Wiggle Subsequence is filed here because LeetCode tags it Greedy, which is the vocabulary this hub collects.

The greedy guide has the Python template for the pattern and the 346 LeetCode problems that use it.

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