525. Contiguous Array

https://leetcode.com/problems/contiguous-array/

Python

Prefix Sum

• first_seem key is difference btw zero_count and one_count, value is the first seem index
• fist_seem inital with 0 -> -1 to ensure the first place able to be calculated from next 0s

class Solution:
    def findMaxLength(self, nums: List[int]) -> int:
        first_seem = {0: -1}

        zero_count = 0
        one_count = 0

        ans = 0

        for index, num in enumerate(nums):
            if num == 0:
                zero_count += 1
            else:
                one_count += 1

            diff = zero_count - one_count
            if diff in first_seem:
                ans = max(ans, index - first_seem[diff])
            else:
                first_seem[diff] = index

        return ans