Question

问题：给定一个非负整数列表，将它们排列成最大数字。

所以给出[1,20,23,4,8]，最大的数字是8423201。

我无法理解以下解决方案：

num.sort(cmp=lambda x, y: cmp(y + x, x + y))做了什么？

为什么它有两个参数x和y？如果输入一个列表，x和y在列表中代表什么？

class Solution:
    # @param num, a list of integers
    # @return a string
    def largestNumber(self, num):
        num = [str(x) for x in num]
        num.sort(cmp=lambda x, y: cmp(y + x, x + y))
        largest = ''.join(num)
        return largest.lstrip('0') or '0'

if __name__ == "__main__":
    num = [3, 30, 34, 5, 9]
    print Solution().largestNumber(num)

有人可以解释代码解决方案吗？感谢。

Answer 1

以下是对代码的解释。

class Solution:
    # @param num, a list of integers
    # @return a string
    def largestNumber(self, num):
        # converts list of numbers to list of strings
        num = [str(x) for x in num]
        # sorts list based on comparator function provided (an "anonymous" lambda function)
        # the comparator is used to compare pairs of elements for sorting (x comes first returns -1, "equal" returns 0, x comes after returns 1)
        # the lambda function takes two arguments x and y because comparator takes two arguments
        # since these are strings, they are compared by seeing which concatenation (+ operator with strings) 
        # comes "first" alphabetically but note the x and y are "swapped" from what you might expect (to reverse the sort)
        num.sort(cmp=lambda x, y: cmp(y + x, x + y))
        # join the sorted list together with empty string separators
        largest = ''.join(num)
        # remove any leading 0s
        return largest.lstrip('0') or '0'

if __name__ == "__main__":
    num = [3, 30, 34, 5, 9]
    print Solution().largestNumber(num)

Answer 2

Python 2.x排序函数允许使用cmp函数来比较两个项目。如果＆lt; cmp(a, b)，则返回-1。 b，如果a == b，则为0;如果a>，则为1;湾

此代码创造性地使用cmp＆＃34;＆＃34;获得所需的排序顺序来解决问题;它将排序＆＃34; 8＆＃34;之前＆＃34; 80＆＃34;因为＆＃34; 880＆＃34; ＆GT; ＆＃34; 808＆＃34;

问题是你想要一个反向字母排序，但是你想要长字符串之前的短字符串（如果它们的前缀相同）。

更通用的解决方案是按字母顺序进行反向排序，但是将所有字符串右键填充到相同的长度 - 至少与您要排序的最长字符串一样长 - 使用一个字符排序为＆＃34;更大比9＆＃34;。

我们如何选择这样的角色？那么，

ord("9")                                         # -> 57
print("".join(chr(ch) for ch in range(57, 75))   # "9:;<=>?@ABCDEFGHIJ"

所以"A"看起来是一个不错的选择，并且很容易记住，因为它的十六进制为10。

然后

def largest_number(nums):
    # convert to strings
    nums = [str(i) for i in nums]

    # find the length of the longest string
    longest = max(len(s) for s in nums)

    # create a function to pad strings to that length
    def padded(s, pad_char="A", length=longest):
        return s + pad_char * (length - len(s))

    # sort the strings greatest-to-least according to their padded values
    nums.sort(key=padded, reverse=True)
    # nums is now ["9", "5", "3", "34", "30"]

    # get the resulting output-string
    num = "".join(nums)

    # remove any leading 0s
    #  (this should only ever occur if all input nums were 0)
    num = num.lstrip("0")

    if num:
        return num
    else:
        # the string was all 0s - return a single 0
        return "0"

if __name__ == "__main__":
    nums = [3, 30, 34, 5, 9]
    print(largest_number(nums))   # -> "9533430"

Answer 3

list.sort(function)使用您指定的function对您的列表进行排序。

列表python

3 个答案: