Leetcode 321. Create Maximum Number

文章作者：Tyan
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1. Description

2. Solution

解析：

1. 首先將問題分解爲兩個子問題，即分別求兩個序列的最大值，得到兩個子序列（保留順序），兩個子序列的長度和爲k。
2. 合併兩個子序列
3. 比較所有合併後的序列，返回值最大的序列

• Version 1

class Solution:
    def maxNumber(self, nums1, nums2, k):
        result = []
        m = len(nums1)
        n = len(nums2)
        for i in range(k + 1):
            if i > m or k - i > n:
                continue
            candidate = self.merge(self.getMaxNumber(nums1, i), self.getMaxNumber(nums2, k - i))
            result = max(result, candidate)
        return result


    def merge(self, nums1, nums2):
        result = []
        while nums1 or nums2:
            if self.compare(nums1, nums2):
                result.append(nums1.pop(0))
            else:
                result.append(nums2.pop(0))
        return result


    def compare(self, nums1, nums2):
        m = len(nums1)
        n = len(nums2)
        min_value = min(m, n)
        for i in range(min_value):
            if nums1[i] > nums2[i]:
                return True
            if nums1[i] < nums2[i]:
                return False

        if m >= n:
            return True
        return False


    def getMaxNumber(self, nums, k):
        nums = nums[:]
        if len(nums) == k:
            return nums
        result = []
        while k > 0:
            length = len(nums)
            max_value = nums[0]
            max_index = 0
            for index, num in enumerate(nums):
                if length - index < k:
                    break
                if num > max_value:
                    max_value = num
                    max_index = index

            nums = nums[max_index + 1:]
            result.append(max_value)
            k -= 1

        return result

• Version 2

class Solution:
    def maxNumber(self, nums1, nums2, k):
        result = []
        m = len(nums1)
        n = len(nums2)
        for i in range(k + 1):
            if i > m or k - i > n:
                continue
            candidate = self.merge(self.getMaxNumber(nums1, i), self.getMaxNumber(nums2, k - i))
            result = max(result, candidate)
        return result


    def merge(self, a, b):
        result = []
        while a or b:
            if self.compare(a, b):
                result.append(a.pop(0))
            else:
                result.append(b.pop(0))
        return result


    def compare(self, a, b):
        if max(a, b) == a:
            return True
        else:
            return False


    def getMaxNumber(self, nums, k):
        nums = nums[:]
        if len(nums) == k:
            return nums
        result = []
        while k > 0:
            length = len(nums)
            max_value = nums[0]
            max_index = 0
            for index, num in enumerate(nums):
                if length - index < k:
                    break
                if num > max_value:
                    max_value = num
                    max_index = index

            nums = nums[max_index + 1:]
            result.append(max_value)
            k -= 1

        return result

• Version 3

class Solution:
    def maxNumber(self, nums1, nums2, k):
        result = []
        m = len(nums1)
        n = len(nums2)
        for i in range(k + 1):
            if i > m or k - i > n:
                continue
            candidate = self.merge(self.getMaxNumber(nums1, i), self.getMaxNumber(nums2, k - i))
            result = max(result, candidate)
        return result


    def merge(self, a, b):
        return [max(a, b).pop(0) for i in range(len(a) + len(b))]


    def getMaxNumber(self, nums, k):
        nums = nums[:]
        if len(nums) == k:
            return nums
        result = []
        while k > 0:
            length = len(nums)
            max_value = nums[0]
            max_index = 0
            for index, num in enumerate(nums):
                if length - index < k:
                    break
                if num > max_value:
                    max_value = num
                    max_index = index

            nums = nums[max_index + 1:]
            result.append(max_value)
            k -= 1

        return result

Reference

1. https://leetcode.com/problems/create-maximum-number/