[LeetCode] 179. The maximum number of

Topic links: https://leetcode-cn.com/problems/largest-number/

Subject description:

Given a set of non-negative integers, their order rearranged so as to form a largest integer.

Example:

Example 1:

输入: [10,2]
输出: 210

Example 2:

输入: [3,30,34,5,9]
输出: 9534330

Description: The output can be quite large, so you need to return a string instead of an integer.

Ideas:

Custom collations

1. usecmp_to_key
2. Magic methods of the class

I can see the details written about Pythonordering summary

---

nArray length

kNumber average length of the string

Because of the complexity of sorting time nlogn

Because there is also a comparison between the strings, so the time complexity is \ (knlogn \)

Space complexity: \ (O (n-) \)

Code:

usecmp_to_key

class Solution:
    def largestNumber(self, nums: List[int]) -> str:
        from functools import cmp_to_key
        def helper(x, y):
            if x + y > y + x:
                return -1
            elif x + y < y + x:
                return 1
            else:
                return 0

        return "".join(sorted(map(str, nums), key=cmp_to_key(helper))).lstrip("0") or "0"

Magic methods of the class, two ways for writing

A wording:

class Solution:
    def largestNumber(self, nums: List[int]) -> str:
        class cmp_large:
            def __init__(self, num):
                self.num = str(num)

            def __lt__(self, other):
                return self.num + other.num > other.num + self.num

            def __gt__(self, other):
                return self.num + other.num < other.num + self.num

            def __eq__(self, other):
                return self.num + other.num == other.num + self.num

        nums = [cmp_large(num) for num in nums]
        return "".join(a.num for a in sorted(nums)).lstrip("0") or "0"

Written two:

class Solution:
    def largestNumber(self, nums: List[int]) -> str:
        class large_num(str):
            def __lt__(self, other):
                return self + other > other + self
        return "".join(sorted(map(str, nums), key=large_num)).lstrip("0") or "0"