Contiguous Array

class Solution:
    def findMaxLength(self, nums: List[int]) -> int:
        res = ps = 0
#ps = no. of ones - no. of zeros
        hm = {0: -1}
        for i, e in enumerate(nums):
            ps += 2*e - 1
            if ps in hm:
                res = max(i-hm[ps], res)
            else:
                hm[ps] = i
        return res