Extract substrings between any pair of delimiters

Given a string str, the task is to extract the substrings present between two delimiters, i.e. '[' and ']'.

Examples:

Input: str = “[This is a string to be extracted]”
Output: This is a string to be extracted
Explanation: The square brackets '[' and ']' serve as delimiters in the given string.

Input: str= "[This is first] ignored text [This is second]"
Output: 
This is first
This is second
Explanation: The square brackets '[' and ']' serve as delimiters in the given string.

Stack-based Approach: Iterate over the characters of the string and insert the index of every '[' encountered into the stack. For every ']' encountered, simply pop the index stored at the top of the stack and print the substring lying in between.

Below is the implementation of the above approach

This is first
This is second

Time Complexity: O(N)
Auxiliary Space: O(N)

Space-Efficient Approach: The idea is to use Regular Expressions to solve this problem. Create a regular expression to extract the string between two delimiters as regex = “\\[(.*?)\\]” and match the given string with the Regular Expression. Print the subsequence formed.

Below is the implementation of the above approach:

This is first
This is second

Time Complexity: O(N)
Auxiliary Space: O(1)