Refactor Nested Repetition Decoder

Refactor a legacy decoder for strings of the form k[encoded_string]. Implement decode_string(s) so it returns the fully expanded string, handles nested brackets, and avoids inefficient repeated rescanning or string concatenation.

Inputs = "3[a]2[bc]"Output"aaabcbc"Why`a` repeats 3 times and `bc` repeats 2 times.

Inputs = "3[a2[c]]"Output"accaccacc"WhyDecode the inner block first, then apply the outer repetition.

Problem

Examples

Example 1

Inputs = "3[a]2[bc]"Output"aaabcbc"Why`a` repeats 3 times and `bc` repeats 2 times.

Example 2

Inputs = "3[a2[c]]"Output"accaccacc"WhyDecode the inner block first, then apply the outer repetition.

Constraints

`1 <= len(s) <= 10^5`
Input contains lowercase letters, digits, `[` and `]`
Repeat counts may be multi-digit
Input is always valid

Problem

Examples

Example 1

Inputs = "3[a]2[bc]"Output"aaabcbc"Why`a` repeats 3 times and `bc` repeats 2 times.

Example 2

Inputs = "3[a2[c]]"Output"accaccacc"WhyDecode the inner block first, then apply the outer repetition.

Constraints

`1 <= len(s) <= 10^5`
Input contains lowercase letters, digits, `[` and `]`
Repeat counts may be multi-digit
Input is always valid

Problem

Examples

Example 1

Inputs = "3[a]2[bc]"Output"aaabcbc"Why`a` repeats 3 times and `bc` repeats 2 times.

Example 2

Inputs = "3[a2[c]]"Output"accaccacc"WhyDecode the inner block first, then apply the outer repetition.

Constraints

`1 <= len(s) <= 10^5`
Input contains lowercase letters, digits, `[` and `]`
Repeat counts may be multi-digit
Input is always valid

Interview Guides

Problem

Examples

Constraints

Problem

Examples

Constraints

Refactor Nested Repetition Decoder

Problem

Examples

Constraints

Problem

Examples

Constraints