[勇者闯LeetCode] 38. Count and Say

[勇者闯LeetCode] 38. Count and Say

Description

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 111221, ...

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.
Given an integer n, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

Information

• Tags: String
• Difficulty: Easy

Solution

class Solution(object):    def countAndSay(self, n):        """        :type n: int        :rtype: str        """        def update(xs):            cnt, val = 1, xs[0]            ans = ""            for x in xs[1:]:                if x == val:                    cnt += 1                else:                    ans += str(cnt) + val                    val = x                    cnt = 1            ans += str(cnt) + val            return ans        s = "1"        for _ in range(1, n):            s = update(s)        return s