decoded-string-at-index.py

# V0 

# V1 
# https://blog.csdn.net/fuxuemingzhu/article/details/81977433
# https://blog.csdn.net/qq_26440803/article/details/84261151
class Solution(object):
    def decodeAtIndex(self, S, K):
        """
        :type S: str
        :type K: int
        :rtype: str
        """
        size = 0
        for c in S:
            if c.isdigit():
                size *= int(c)
            else:
                size += 1

        for c in reversed(S):
            K %= size
            if K == 0 and c.isalpha():
                return c
            if c.isdigit():
                size /= int(c)
            else:
                size -= 1

# V2 
# Time:  O(n)
# Space: O(1)
class Solution(object):
    def decodeAtIndex(self, S, K):
        """
        :type S: str
        :type K: int
        :rtype: str
        """
        i = 0
        for c in S:
            if c.isdigit():
                i *= int(c)
            else:
                i += 1

        for c in reversed(S):
            K %= i
            if K == 0 and c.isalpha():
                return c

            if c.isdigit():
                i /= int(c)
            else:
                i -= 1