#3612

Medium

LeetCode Problem Workspace

Process String with Special Operations I

Simulate a series of operations on a string to transform it into the desired result using special characters.

Problem Statement

You are given a string consisting of lowercase English letters and special characters: *, #, and %. Process this string from left to right, applying specific operations for each character. When encountering a letter, it is added to the result string. Special characters such as # and % influence the result in different ways, while * acts as a reset mechanism.

The task is to simulate the operations based on the string and return the final result after processing all characters. Carefully handle the impact of each special character to ensure the correct outcome, as seen in the examples provided.

Examples

Example 1

Input: s = "a#b%*"

Output: "ba"

Thus, the final result is "ba" .

Example 2

Input: s = "z*#"

Output: ""

Thus, the final result is "" .

Constraints

1 <= s.length <= 20
s consists of only lowercase English letters and special characters *, #, and %.

Solution Approach

Simulate the String Processing

Iterate over the string character by character. For each letter, append it to the result. Handle each special character by applying the rules: for example, # can remove the last letter, and * resets the result string.

Use a Stack-like Approach

A stack structure can be utilized to simulate the process more effectively, pushing characters and popping them when needed (such as when encountering #). This approach ensures that the string transformations are applied in the correct order.

Consider Time and Space Complexity

Keep track of both time and space complexities to ensure the solution is optimal. With the given constraints, processing the string in a linear pass with a manageable amount of memory will be efficient.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

The time complexity is O(n), where n is the length of the string, as we only iterate over the string once. The space complexity is O(n), as we store the resulting characters in a stack-like structure to simulate the transformations.

What Interviewers Usually Probe

The candidate's approach to handling special characters efficiently will be crucial.
Watch for edge case handling, especially with consecutive special characters or empty results.
Evaluate the candidate's ability to simplify string transformations and optimize space usage.

Common Pitfalls or Variants

Common pitfalls

Forgetting to handle consecutive special characters or operations like * correctly.
Not considering edge cases, such as when the string starts or ends with special characters.
Inefficient handling of the string leading to higher time or space complexities.

Follow-up variants

Modify the rules for * and # to have different effects (e.g., # removes multiple previous characters).
Process the string in reverse order and observe any difference in the final result.
Introduce additional special characters to simulate more complex string transformations.

FAQ

What are the key operations to simulate in the "Process String with Special Operations I" problem?

The key operations involve handling special characters such as *, #, and %, which alter the state of the resulting string during the simulation.

How can I handle consecutive special characters in this problem?

Ensure you account for the impact of each special character individually, using a stack-like structure to manage transformations.

What is the most efficient way to process the string in this problem?

A linear pass over the string with careful handling of special characters is the most efficient approach, achieving O(n) time complexity.

How do I deal with edge cases in "Process String with Special Operations I"?

Consider cases like strings starting with or ending with special characters, as well as handling consecutive operations like * or #.

What if I encounter multiple * or # characters in sequence?

Handle each * and # individually, ensuring that * resets the result and # correctly removes the last character as per the problem's rules.

terminal

Solution

Solution 1: Simulation

We can directly simulate the operations described in the problem. We use a list $\text{result}$ to store the current result string. For each character in the input string $s$, we perform the corresponding operation based on the character type:

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class Solution:
    def processStr(self, s: str) -> str:
        result = []
        for c in s:
            if c.isalpha():
                result.append(c)
            elif c == "*" and result:
                result.pop()
            elif c == "#":
                result.extend(result)
            elif c == "%":
                result.reverse()
        return "".join(result)

Continue Practicing

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