Question

Given a string consisting of substring Pi in parentheses followed by a number Ni in curly brackets, the string is expanded such that the substring Pi is repeatedly concatenated Ni number of times. For example, in the given string: (ab(d){3}){2}, the string is expanded as:

Step 1: (ab(d){3}){2} -> (abddd){2}
Step 2: (abddd){2} -> abdddabddd

Write an algorithm to find the expanded string.

Answer 1

The given string (ab(d){3}){2} can be expanded using a specific algorithm that recursively processes the pattern, pushing and popping states from a stack to build the expanded string abdddabddd.

Step-by-step explanation:

To write an algorithm that processes a string containing substrings and numbers indicating how many times those substrings should be repeated, we follow a series of steps. The example given is (ab(d){3}){2}, which expands to abdddabddd.

1. Initialize an empty string for the output.
2. Scan the input string from left to right.
3. Each time an opening parenthesis ( is encountered, push the current state on a stack.
4. Append characters to the current string until a closing parenthesis ) or a curly bracket { is found.
5. When a closing parenthesis ) is encountered, look ahead for a number inside curly brackets to determine the repetition count.
6. Pop the last state from the stack and concatenate the current string with step 5's repetition count.
7. Repeat steps 3 to 6 for any additional substring patterns.
8. Return the fully expanded string.

By following this algorithm, we can expand any similar complex string pattern into its full form.