Maximum Size Subarray Sum Equals k — Python

# Time:  O(n)
# Space: O(n)

class Solution(object):
    def maxSubArrayLen(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: int
        """
        sums = {}
        cur_sum, max_len = 0, 0
        for i in xrange(len(nums)):
            cur_sum += nums[i]
            if cur_sum == k:
                max_len = i + 1
            elif cur_sum - k in sums:
                max_len = max(max_len, i - sums[cur_sum - k])
            if cur_sum not in sums:
                sums[cur_sum] = i  # Only keep the smallest index.
        return max_len