38. Count and Say

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The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     1
2.     11
3.     21
4.     1211
5.     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 where 1 ≤ n ≤ 30, generate the n^th term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

解法

class Solution:
    def countAndSay(self, n) :
        
        if n==1:   
            return '1'
        elif n==2:
            return '11'
        data=self.countAndSay(n-1)
        count=dict()
        result=''
        tmp_char=''
        for x in range(len(data)):
            if not tmp_char:
                tmp_char=data[x]
                count[data[x]]=1
                continue
            if data[x]==tmp_char:
                count[data[x]]+=1
            else:
                result+=str(count[tmp_char])+tmp_char
                tmp_char=data[x]
                count[data[x]]=1
            if x==len(data)-1 :
                 result+=str(count[tmp_char])+tmp_char
          
        return result

发表至：leetcode

2019-02-13

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