38. Count and Say leetcode python 2016 new season

原创于 2016-01-21 13:09:24 发布 · 394 阅读

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本文详细介绍了计数与说序列算法的核心概念，通过实例演示如何生成指定位置的序列值，适合对算法和字符串操作感兴趣的读者深入理解。

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.

class Solution(object):
    def countAndSay(self, n):
        """
        :type n: int
        :rtype: str
        """
        if n == 1:
            return '1'
        else:
            prev = self.countAndSay(n - 1)
            start = 0
            res = ''
            while start < len(prev):
                count = 0
                cur = prev[start]
                while start < len(prev) and cur == prev[start]:
                    start += 1
                    count += 1
                res += str(count) + cur
            return res