leetcood学习笔记-38-报数

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题目描述：

第一次提交：

class Solution:
    def countAndSay(self, n: int) -> str:
        f = ""
        for i in range(n-1):
            count = 0
            c = ''
            for j in range(len(f)):
                if j == 0 or (j - 1 > -1 and f[j]==f[j-1]):
                    count += 1
                else:
                    c += str(count) + f[j - 1]
                    count = 1
            c += str(count) + f[j]
            i += 1
            f = c;

        return f

方法二：递归

def countAndSay(self, n: int) -> str:
        def count(n, str_num):
            if n <= 1:
                return str_num
            new_str_num = ""
            cnt, old = 1, str_num[0]
            for ch in str_num[1:]:
                if ch != old:
                    new_str_num += str(cnt) + old
                    cnt, old = 1, ch
                else:
                    cnt += 1
            if cnt:
                new_str_num += str(cnt) + str_num[-1]
            return count(n-1, new_str_num)
        return count(n, "")