How should I practice Decode an Encoded String?

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Decode an Encoded String

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Problem statement

An encoded string uses positive repeat counts followed by bracketed segments. Decode it using these rules:

k[segment] means the decoded segment is repeated exactly k times.
Segments may be nested.
Letters outside brackets appear once and remain in order.

Return the fully decoded string.

Function

decodeString(s: String) → String

Examples

Example 1

s = "3[a2[c]]"return = "accaccacc"

The inner block becomes acc, then the outer count repeats it three times.

Example 2

s = "2[ab]3[c]"return = "ababccc"

The two adjacent encoded blocks decode independently and are concatenated.

Constraints

1 <= s.length <= 10^4
s is a well-formed encoding made of lowercase English letters, digits, and brackets.
Every repeat count is between 1 and 300.
The decoded string has at most 10^5 characters.