LeetCode38. 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 nth term of the count-and-say sequence.

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

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<思路>题看着比较烦，只能一步步读数。cur_val是当前要读的数（一位），count是这个数的个数，part算是中间变量，保存的是这一次循环的count和cur_val(几个几)。

class Solution(object):
    def countAndSay(self, n):
        """
        :type n: int
        :rtype: str
        """
        num = '1'
        
        while n>1:
            cur_val = num[0]
            count = 0
            part = ''
            
            for j in num:
                if cur_val == j:
                    count += 1
                else:
                    part += str(count)+cur_val
                    cur_val = j
                    count = 1
            
            part += str(count) + cur_val
            num = part
            n -= 1
        return num