525. Contiguous Array - Explanation

class Solution:
    def findMaxLength(self, nums: List[int]) -> int:
        n, res = len(nums), 0

        for i in range(n):
            zeros = ones = 0
            for j in range(i, n):
                if nums[j] == 1:
                    ones += 1
                else:
                    zeros += 1

                if ones == zeros and res < (j - i + 1):
                    res = j - i + 1

        return res

class Solution:
    def findMaxLength(self, nums: List[int]) -> int:
        n = len(nums)
        res = 0
        diff_index = [None] * (2 * n + 1)
        count = 0

        for i in range(n):
            count += 1 if nums[i] == 1 else -1
            if count == 0:
                res = i + 1
            if diff_index[count + n] is not None:
                res = max(res, i - diff_index[count + n])
            else:
                diff_index[count + n] = i

        return res

class Solution:
    def findMaxLength(self, nums: List[int]) -> int:
        zero = one = res = 0
        diff_index = {}

        for i, n in enumerate(nums):
            if n == 0:
                zero += 1
            else:
                one += 1

            if one - zero not in diff_index:
                diff_index[one - zero] = i

            if one == zero:
                res = one + zero
            else:
                idx = diff_index[one - zero]
                res = max(res, i - idx)

        return res