An encoded string S is given. To find and write the decoded string to a tape, the encoded string is read one character at a time and the following steps are taken:
If the character read is a letter, that letter is written onto the tape. If the character read is a digit (say d), the entire current tape is repeatedly written d-1 more times in total. Now for some encoded string S, and an index K, find and return the K-th letter (1 indexed) in the decoded string.
Example 1:
Input: S = "leet2code3", K = 10
Output: "o"
Explanation:
The decoded string is "leetleetcodeleetleetcodeleetleetcode".
The 10th letter in the string is "o".
Example 2:
Input: S = "ha22", K = 5
Output: "h"
Explanation:
The decoded string is "hahahaha". The 5th letter is "h".
Example 3:
Input: S = "a2345678999999999999999", K = 1
Output: "a"
Explanation:
The decoded string is "a" repeated 8301530446056247680 times. The 1st letter is "a".
Note:
- 2 <= S.length <= 100
- S will only contain lowercase letters and digits 2 through 9.
- S starts with a letter.
- 1 <= K <= 10^9
- The decoded string is guaranteed to have less than 2^63 letters.
给定一个编码字符串 S。为了找出解码字符串并将其写入磁带,从编码字符串中每次读取一个字符,并采取以下步骤:
- 如果所读的字符是字母,则将该字母写在磁带上。
- 如果所读的字符是数字(例如 d),则整个当前磁带总共会被重复写 d-1 次。
现在,对于给定的编码字符串 S 和索引 K,查找并返回解码字符串中的第 K 个字母。
按照题意,扫描字符串扫到数字的时候,开始重复字符串,这里可以用递归。注意在重复字符串的时候到第 K 个字符的时候就可以返回了,不要等所有字符都扩展完成,这样会超时。d 有可能超大。