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  • 376. Wiggle Subsequence

    A sequence of numbers is called a wiggle sequence if 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 fewer than two elements is trivially a wiggle sequence.

    For example, [1,7,4,9,2,5] is a wiggle sequence because the differences (6,-3,5,-7,3) are alternately positive and negative. In contrast, [1,4,7,2,5] and [1,7,4,5,5] are not wiggle sequences, the first because its first two differences are positive and the second because its last difference is zero.

    Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence. A subsequence is obtained by deleting some number of elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order.

    Example 1:

    Input: [1,7,4,9,2,5]
    Output: 6
    Explanation: The entire sequence is a wiggle sequence.

    Example 2:

    Input: [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].

    Example 3:

    Input: [1,2,3,4,5,6,7,8,9]
    Output: 2

    Follow up:
    Can you do it in O(n) time?

    class Solution(object):
        def wiggleMaxLength(self, nums):
            """
            :type nums: List[int]
            :rtype: int
            """
            
            n = len(nums)
            if n == 0:
                return 0
            
            up = 1
            down = 1
            
            for i in range(1,n):
                if nums[i] > nums[i-1]:
                    up = down + 1
                elif nums[i] < nums[i-1]:
                    down = up + 1
            return max(up, down)
                    
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  • 原文地址:https://www.cnblogs.com/boluo007/p/12547334.html
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