Count and Say

Question

• leetcode: Count and Say | LeetCode OJ
• lintcode: (420) Count and Say

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.

Example
Given n = 5, return "111221".

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

题解

题目大意是找第 n 个数(字符串表示)，规则则是对于连续字符串，表示为重复次数+数本身。

• reference
• visualization

class Solution:
    # @return a string
    def count(self,s):
        t=''; count=0; curr='#'
        for i in s:
            if i!=curr:
                if curr!='#':
                    t+=str(count)+curr
                curr=i
                count=1
            else:
                count+=1
        t+=str(count)+curr
        return t
    def countAndSay(self, n):
        s='1'
        for i in range(2,n+1):
            s=self.count(s)
        return s