create-maximum-number.py

# Time:  O(k * (m + n + k)) ~ O(k * (m + n + k^2))
# Space: O(m + n + k^2)

class Solution(object):
    def maxNumber(self, nums1, nums2, k):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :type k: int
        :rtype: List[int]
        """
        def get_max_digits(nums, start, end, max_digits):
            max_digits[end] = max_digit(nums, end)
            for i in reversed(xrange(start, end)):
                max_digits[i] = delete_digit(max_digits[i + 1])

        def max_digit(nums, k):
            drop = len(nums) - k
            res = []
            for num in nums:
                while drop and res and res[-1] < num:
                    res.pop()
                    drop -= 1
                res.append(num)
            return res[:k]

        def delete_digit(nums):
            res = list(nums)
            for i in xrange(len(res)):
                if i == len(res) - 1 or res[i] < res[i + 1]:
                    res = res[:i] + res[i+1:]
                    break
            return res

        def merge(a, b):
            return [max(a, b).pop(0) for _ in xrange(len(a)+len(b))]

        m, n = len(nums1), len(nums2)

        max_digits1, max_digits2 = [[] for _ in xrange(k + 1)], [[] for _ in xrange(k + 1)]
        get_max_digits(nums1, max(0, k - n), min(k, m), max_digits1)
        get_max_digits(nums2, max(0, k - m), min(k, n), max_digits2)

        return max(merge(max_digits1[i], max_digits2[k-i]) \
                   for i in xrange(max(0, k - n), min(k, m) + 1))