880 - Decoded String at Index\.

Medium

You are given an encoded string s. To decode the 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 d, the entire current tape is repeatedly written d - 1 more times in total.

Given an integer k, return the <code>k^th</code> letter ( 1-indexed) in the decoded string.

Example 1:

Input: s = "leet2code3", k = 10

Output: "o"

Explanation: The decoded string is "leetleetcodeleetleetcodeleetleetcode". The 10^th letter in the string is "o".

Example 2:

Input: s = "ha22", k = 5

Output: "h"

Explanation: The decoded string is "hahahaha". The 5^th letter is "h".

Example 3:

Input: s = "a2345678999999999999999", k = 1

Output: "a"

Explanation: The decoded string is "a" repeated 8301530446056247680 times. The 1^st letter is "a".

Constraints:

• 2 <= s.length <= 100

• s consists of lowercase English letters and digits 2 through 9.

• s starts with a letter.

• <code>1 <= k <= 10⁹</code>

• It is guaranteed that k is less than or equal to the length of the decoded string.

• The decoded string is guaranteed to have less than <code>2⁶³</code> letters.