Scale Engineer

Goal Parser Interpretation

Easy
#1539Time: O(N), where N is the length of the command string. Although `replace()` is called twice, each call scans the string. In Java, `String.replace()` creates a new string, so the total time is proportional to the length of the string for each operation, resulting in a linear time complexity.Space: O(N), where N is the length of the command string. This is because strings in Java are immutable. Each call to `replace()` can potentially create a new string of length up to N, leading to space usage for the intermediate and final strings.
Data structures
String

Prompt

You own a Goal Parser that can interpret a string command. The command consists of an alphabet of "G", "()" and/or "(al)" in some order. The Goal Parser will interpret "G" as the string "G", "()" as the string "o", and "(al)" as the string "al". The interpreted strings are then concatenated in the original order.

Given the string command, return the Goal Parser's interpretation of command.

 

Example 1:

Input: command = "G()(al)"
Output: "Goal"
Explanation: The Goal Parser interprets the command as follows:
G -> G
() -> o
(al) -> al
The final concatenated result is "Goal".

Example 2:

Input: command = "G()()()()(al)"
Output: "Gooooal"

Example 3:

Input: command = "(al)G(al)()()G"
Output: "alGalooG"

 

Constraints:

  • 1 <= command.length <= 100
  • command consists of "G", "()", and/or "(al)" in some order.

Approaches

2 approaches with complexity analysis and trade-offs.

This approach leverages the built-in replace() method of the String class. It's a very direct and high-level way to solve the problem. We simply replace all occurrences of "()" with "o" and then all occurrences of "(al)" with "al".

Algorithm

    1. Take the input command string.
    1. Use the String.replace() method to substitute all occurrences of "()" with "o". This creates a new intermediate string.
    1. On the intermediate string, use the String.replace() method again to substitute all occurrences of "(al)" with "al".
    1. Return the final resulting string.

Walkthrough

This method is the most straightforward due to its use of high-level string manipulation functions. The logic is simple: perform a series of replacements on the original string until all special sequences are converted to their interpretations. While easy to write, it's not the most performant solution because string immutability in Java means each replacement operation creates a new string in memory.

class Solution {    public String interpret(String command) {        // First, replace all occurrences of "()" with "o"        String result = command.replace("()", "o");        // Then, replace all occurrences of "(al)" with "al"        result = result.replace("(al)", "al");        return result;    }}

Complexity

Time

O(N), where N is the length of the command string. Although `replace()` is called twice, each call scans the string. In Java, `String.replace()` creates a new string, so the total time is proportional to the length of the string for each operation, resulting in a linear time complexity.

Space

O(N), where N is the length of the command string. This is because strings in Java are immutable. Each call to `replace()` can potentially create a new string of length up to N, leading to space usage for the intermediate and final strings.

Trade-offs

Pros

  • Extremely simple and concise to write.

  • Highly readable and easy to understand for other developers.

Cons

  • Creates intermediate string objects, which can be inefficient in terms of memory and performance, especially for very large input strings.

  • Involves multiple passes over the string data, making it theoretically slower than a single-pass solution.

Solutions

class Solution { public String interpret ( String command ) { return command . replace ( "()" , "o" ). replace ( "(al)" , "al" ); } }

Video walkthrough

Newsletter

One sharp idea, every week

System design and interview prep — short enough to finish.

No spam. Unsubscribe anytime.

Practice

Same difficulty — related problems to reinforce the pattern.

← Previous

Previous problem

Next →

Next problem