class Solution:
    def findMaxLength(self, nums: List[int]) -> int:
        N = len(nums)
        deltas = {0: 0}
        ans = 0

        cur_delta = 0
        for i, n in enumerate(nums):
            cur_delta += 1 if n == 1 else -1
            if cur_delta not in deltas:
                deltas[cur_delta] = i + 1

            if cur_delta in deltas:
                ans = max(ans, i + 1 - deltas[cur_delta])
        return ans