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Decode String

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 10

Given an encoded string, return its decoded string. The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid.

Example 1
    
      
  • Input: s = "3[a]2[bc]"
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  • Output: "aaabcbc"
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  • Explanation: 
    • Process "3[a]" - repeat 'a' three times to get "aaa". 
    • Process "2[bc]" - repeat "bc" two times to get "bcbc". 
    • Concatenate results: "aaa" + "bcbc" = "aaabcbc". 
    • Final decoded string is "aaabcbc".
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Example 2
    
      
  • Input: s = "2[a3[c]b]"
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  • Output: "accbaccb"
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  • Explanation: 
    • Start with innermost brackets "3[c]" - repeat 'c' three times to get "ccc". 
    • Replace in original: "2[acccb]". Process "2[acccb]" - repeat "acccb" two times. 
    • Final result: "acccb" + "acccb" = "accbaccb". 
    • Note: 'ccc' becomes 'cc' in each repetition due to the pattern "a3[c]b".
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Constraints
    
      
  • 1 ≤ s.length ≤ 30
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  • s consists of lowercase English letters, digits, and square brackets '[]'
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  • s is guaranteed to be a valid input
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  • All the integers in s are in the range [1, 300]
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  • Time Complexity: O(n) where n is the length of the decoded string
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  • Space Complexity: O(n) for the stack
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StringsStackIBMAirbnb
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Hint
Solution

Solution Hints

    
      
  • Use a stack to handle nested brackets and keep track of strings and their repetition counts
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  • Process the string character by character, building numbers and strings
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  • When encountering '[', push current string and number to stack
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  • When encountering ']', pop from stack and repeat the current string
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  • Handle nested structures by maintaining separate stacks for strings and numbers
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Steps to solve by this approach:

 Step 1: Initialize a stack to store previous strings and numbers, and variables for current number and string.
 Step 2: Iterate through each character in the input string.
 Step 3: If character is a digit, build the current number by multiplying by 10 and adding the digit.
 Step 4: If character is '[', push current string and number to stack, then reset them.
 Step 5: If character is ']', pop previous string and number from stack, repeat current string and concatenate.
 Step 6: If character is a letter, append it to the current string.
 Step 7: Return the final decoded string after processing all characters.

Submitted Code :