Decode String

Problem

Decode a string with repeated blocks written in k[encoded] form.

The encoded part inside brackets is repeated k times and blocks may nest. Use a stack of previously built strings and repeat counts: digits accumulate into the current count, an opening bracket saves the state, and a closing bracket pops and repeats the current string.

Return the fully decoded string.

Hint

Push the string built so far and the repeat count when entering a bracket; multiply on exit.

Test cases

case 1

in: ["3[a]2[bc]"]

expected: "aaabcbc"

case 2

in: ["3[a2[c]]"]

expected: "accaccacc"

case 3

in: ["2[abc]3[cd]ef"]

expected: "abcabccdcdcdef"

case 4

in: ["10[a]"]

expected: "aaaaaaaaaa"

case 5

in: ["abc"]

expected: "abc"

Starter codePython

def decode_string(s):
    # Your code here
    pass

5 test cases · run your code against them in the editor