字典中x in dict 和 x in dict.keys()速度不同，前者最快

class Solution(object):
    def findMaxLength(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        # 长度2-》1
        # 长度3-》0
        # 长度4-》2
        # 长度5-》0
        # 长度6-》3
        # 1 2 3 4  5
        
        d = {0: -1}
        sum_ = 0
        res = 0
        for i in range(len(nums)):
            if nums[i] == 0:
                sum_ = sum_ -1
            else:
                sum_ = sum_ + 1
            if sum_ in d.keys():
                
                res = max(res, i - d[sum_])
            else:
                d[sum_] =  d.get(sum_, 0) + i
        return res