#0264

Decode String

MediumDSA28 min20 XP

Problem

Decode strings where k[encoded] means encoded is repeated k times. Inputs are valid and may be nested.

Why This Matters

Decode String is a stack parsing problem that teaches how to preserve previous context before entering brackets.

Function Signature

def decode_string(s):

Examples

Example 1

Inputs = "3[a2[c]]"

Output"accaccacc"

a2[c] becomes acc, then it repeats three times.

Constraints

Return the exact requested value.
Handle edge cases cleanly.
Use the intended DSA pattern when brute force would scale poorly.

CodePython

def decode_string(s):
    """
    Input example: s = "3[a2[c]]"
    Return: "accaccacc"
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return ""

def decode_string(s):
    """
    Input example: s = "3[a2[c]]"
    Return: "accaccacc"
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return ""

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Nested repeat

Input"3[a2[c]]"

Expected"accaccacc"

Decode the inner bracket before the outer bracket.

Multi-digit repeat

Input"10[a]"

Expected"aaaaaaaaaa"

The repeat count can have more than one digit.

Hidden Test Categories

multiple bracket groupsplain letters outside bracketsdeeply nested groups