Leetcode 179. Largest Number

Description: Given a list of non-negative integers nums, arrange them such that they form the largest number.

Note: The result may be very large, so you need to return a string instead of an integer.

Link: 179. Largest Number

Examples:

Example 1:
Input: nums = [10,2]
Output: "210"

Example 2:
Input: nums = [3,30,34,5,9]
Output: "9534330"

Example 3:
Input: nums = [1]
Output: "1"

Example 4:
Input: nums = [10]
Output: "10"

思路: 重点在于如何比较两个数，在题目的设定下，什么样的数字应该是大的，应该排在前面。xy连接起来大于yx，那么x就是大的。所以任何排序算法都可以用，只是将平常的数字大小比较换成题目中的compare. 试一下冒泡：

class Solution(object):
    def largestNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: str
        """
        if len(nums) <= 1:
            return str(nums[0])
        for i in range(len(nums)-1):
            for j in range(i+1, len(nums)):
                if self.compare(nums[i], nums[j]):
                    nums[i], nums[j] = nums[j], nums[i]
        res = ''
        for s in nums[::-1]:
            res += str(s) 
        if res == len(res) * '0':
            return '0'
        return res     
            
    def compare(self, x, y):
        xy = int(str(x)+str(y))
        yx = int(str(y)+str(x))
        if xy >= yx:
            return True
        return False

归并排序：

class Solution(object):
    def largestNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: str
        """
        if len(nums) <= 1:
            return str(nums[0])
        sortnums = self.sortlist(nums)
        res = ''
        for s in sortnums:
            res += str(s) 
        if res == len(res) * '0':
            return '0'
        return res 
    
    def sortlist(self, nums):
        if len(nums) == 1:
            return nums
        mid = len(nums) // 2
        return self.merge(self.sortlist(nums[:mid]), self.sortlist(nums[mid:]))
    
    def merge(self, left, right):
        res = []
        while len(left) > 0 and len(right) > 0:
            if self.compare(left[0], right[0]):
                res.append(left.pop(0))
            else:
                res.append(right.pop(0))
        res += left
        res += right
        return res
        
        
        
    def compare(self, x, y):
        xy = int(str(x)+str(y))
        yx = int(str(y)+str(x))
        if xy >= yx:
            return True
        return False

日期: 2021-03-31  又是阴天，和心情一样糟糕。