K-Concatenation Maximum Sum — Python

# Time:  O(n)
# Space: O(1)

class Solution(object):
    def kConcatenationMaxSum(self, arr, k):
        """
        :type arr: List[int]
        :type k: int
        :rtype: int
        """
        def max_sub_k_array(arr, k):
            result, curr = float("-inf"), float("-inf")
            for _ in xrange(k):
                for x in arr:
                    curr = max(curr+x, x)
                    result = max(result, curr)
            return result
        
        MOD = 10**9+7
        if k == 1:
            return max(max_sub_k_array(arr, 1), 0) % MOD
        return (max(max_sub_k_array(arr, 2), 0) + (k-2)*max(sum(arr), 0)) % MOD