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Decode String
Given an encoded string, return its decoded version.
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; there are no extra white spaces, square brackets are well-formed, etc. Furthermore, you may assume that the original data does not contain any digits and that digits are only for those repeat numbers, k. For example, there will not be input like 3a or 2[4].
The test cases are generated so that the length of the output will never exceed 10^5.
Examples
Constraints
- 1 <= s.length <= 30
- s consists of lowercase English letters, digits, and square brackets '[]'.
- s is guaranteed to be a valid input.
- All the integers in s are in the range [1, 300].
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Your approach
- Pattern:Stack
- Time:O(N)
- Space:O(1)
Complete approach — pattern and complexity both named.
Coach
What you got right
You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.
Where it diverged
No divergence detected. The code correctly aligns with the stated approach.
Next attempt: focus on
Try solving related sliding window problems to build familiarity with two-pointer variants.
Signals
No signals fired — clean run, you stayed in flow.