Leetcode 3201. Find the Maximum Length of Valid Subsequence I

  • [Leetcode 3201. Find the Maximum Length of Valid Subsequence I](#Leetcode 3201. Find the Maximum Length of Valid Subsequence I)
    • [1. 解题思路](#1. 解题思路)
    • [2. 代码实现](#2. 代码实现)

1. 解题思路

这一题我们注意到,要使得条件成立,那么选择出来的数列在奇数位和偶数位上的数字奇偶性必然相同,因此,我们只需要讨论以下4种情况就行了:

  1. 全为奇数
  2. 全为偶数
  3. 先奇数后偶数
  4. 先偶数后奇数

我们分别讨论一下这四种情况然后取出最大值即可。

2. 代码实现

给出python代码实现如下:

python 复制代码
class Solution:
    def maximumLength(self, nums: List[int]) -> int:
        n = len(nums)
        n1 = len([x for x in nums if x % 2 == 0])
        n2 = len([x for x in nums if x % 2 == 1])
        n3, tgt = 0, 0
        for x in nums:
            if x % 2 == tgt:
                n3 += 1
                tgt = 1-tgt
        n4, tgt = 0, 1
        for x in nums:
            if x % 2 == tgt:
                n4 += 1
                tgt = 1-tgt
        return max(n1, n2, n3, n4)

提交代码评测得到:耗时632ms,占用内存39.6MB。

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