题目

1567. Maximum Length of Subarray With Positive Product

解法1：动态规划

键要能想到正数和负数的个数是相互转化的，比如之前是正的序列，加上个正数还是正，加上负数就变负数了，所以需要同时记录当前的正数序列的长度和负数序列的长度

class Solution:
    def getMaxLen(self, nums: List[int]) -> int:
        posi = [0] * len(nums)
        nega = [0] * len(nums)
        if nums[0] > 0:
            posi[0] = 1
        if nums[0] < 0:
            nega[0] = 1
        for i in range(1,len(nums)):
            if nums[i] < 0:
                posi[i] = nega[i-1] + 1 if nega[i-1] > 0 else 0
                nega[i] = posi[i-1] + 1
            elif nums[i] > 0:
                nega[i] = nega[i-1] + 1 if nega[i-1] > 0 else 0
                posi[i] = posi[i-1] + 1
        return max(posi)
                
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解法2:压缩版动态规划

class Solution:
    def getMaxLen(self, nums: List[int]) -> int:
        posi_len = 0
        nega_len = 0
        ans = 0
        for num in nums:
            if num == 0:
                posi_len = nega_len = 0
            elif num < 0:
                posi_len,nega_len = nega_len,posi_len
                nega_len += 1
                if posi_len > 0:
                    posi_len += 1
            else:
                posi_len += 1
                if nega_len > 0:
                    nega_len += 1
            ans = max(ans,posi_len)
        return ans
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