外观数列

class Solution:
    def countAndSay(self, n: int) -> str:
        
        if n == 1:
            return "1"
        else:
            return self.nextItem(self.countAndSay(n-1))
        
    
    def nextItem(self, string: str):
        result = ""
        times = 1
        lens = len(string)
        for i, s in enumerate(string):
            if i + 1 < lens and s != string[i + 1]:
                result += str(times) + s
                times = 1
            elif i + 1 == lens:
                result += str(times) + s
            else:
                times += 1
                
        return result

递归解法，nextItem就是转移函数