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Goal Parser Interpretation

Easy

Asked by:

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Topics:

Strings

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.

Try coding it in LeetCode

Goal Parser Interpretation

Easy

Asked by:

23 views

Topics:

Strings

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.

Try coding it in LeetCode

Solution

Clarifying Questions

When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:

What characters will the input string `command` contain besides 'G', '()', and '(al)'?
Is the input string `command` guaranteed to be a valid sequence of the given interpretations, or could it contain invalid sequences?
Can the input string `command` be empty or null?
Is the case of the input string `command` significant? (e.g., should 'g' be treated the same as 'G')
What is the maximum possible length of the input string `command`?

Brute Force Solution

Approach

We need to translate a coded message. The brute force method simply goes through the message character by character, checking for specific patterns.

Here's how the algorithm would work step-by-step:

Look at the first character in the message.
If it's a 'G', we know it means 'G'.
If it's a '(', we need to look at the next character to see if it's part of '(al)' or '()'.
If it's followed by a ')', then the '()' pattern translates to 'o'.
If it's followed by 'al)', then the '(al)' pattern translates to 'al'.
Continue this process, character by character, replacing each pattern with its translation until we reach the end of the message.

Code Implementation

def interpret_goal_parser(command):    interpreted_string = ""    index = 0
    while index < len(command):
        # If we see a 'G', just add it to the result. 
        if command[index] == 'G':
            interpreted_string += 'G'
            index += 1
        elif command[index] == '(':            # Check if it's '()' or '(al)' 
            if command[index + 1] == ')':
                interpreted_string += 'o'
                index += 2
            else:
                # Handle the '(al)' case. 
                interpreted_string += 'al'
                index += 4
        
        else:
            index += 1

    return interpreted_string

Big(O) Analysis

Time Complexity

O(n) – The algorithm iterates through the input string 'command' of length n exactly once. During each iteration, it performs a constant amount of work, primarily involving character comparisons and string concatenation. There are no nested loops or recursive calls. Thus, the time complexity is directly proportional to the length of the input string, making it O(n).

Space Complexity

O(N) – The algorithm constructs a new string to store the translated message. In the worst-case scenario, where the input 'command' consists entirely of the pattern 'G', the translated string will have the same length as the input. Therefore, the auxiliary space required to store the translated message grows linearly with the size of the input string N, where N is the length of the input string. Thus, the space complexity is O(N).

Optimal Solution

Approach

The most efficient way to interpret the goal command is to read it character by character and translate it as you go. Instead of looking for complex patterns, focus on what each specific piece means and build the result directly.

Here's how the algorithm would work step-by-step:

Start at the beginning of the command string.
Read one character at a time.
If you see a 'G', directly add 'G' to your result.
If you see '()', directly add 'o' to your result.
If you see '(al)', directly add 'al' to your result.
Continue until you reach the end of the command string. The translated string will be complete.

Code Implementation

def interpret_goal_parser(command): 
    interpreted_string = ""
    index = 0
    command_length = len(command)

    while index < command_length:
        # Check for 'G' to add 'G' to output.
        if command[index] == 'G':
            interpreted_string += 'G'
            index += 1

        # Check for '()' to add 'o' to output.
        elif command[index] == '(' and command[index + 1] == ')':
            interpreted_string += 'o'
            index += 2

        #The remaining option must be (al) so we add "al" to the output
        else:
            interpreted_string += 'al'
            index += 4

    return interpreted_string

Big(O) Analysis

Time Complexity

O(n) – The provided solution iterates through the input string 'command' of size n, one character at a time. For each character, it performs a constant amount of work: checking its value and appending a corresponding string to the result. Since the number of operations is directly proportional to the length of the input string, the time complexity is O(n).

Space Complexity

O(N) – The algorithm builds a new string to store the translated command. The size of this translated string can grow up to N, where N is the length of the input command string. In the worst-case scenario, the input string consists only of 'G' characters, resulting in an output string of the same length as the input. Therefore, the auxiliary space required is proportional to the length of the input string, N.

Edge Cases

Case	How to Handle
Null or empty goal string	Return an empty string immediately, as there is nothing to parse.
Goal string contains only 'G'	The interpreter should return 'G' itself, as there are no parentheses to interpret.
Goal string contains only '()'	The interpreter should return 'o' repeated for each '()'.
Goal string contains only '(al)'	The interpreter should return 'al' repeated for each '(al)'.
Goal string starts or ends with an incomplete sequence like '(' or '(a'	The interpreter should ignore or return an error string depending on requirements; a robust implementation might throw an exception or log an error and continue.
Goal string with mixed valid and invalid sequences, e.g., 'G()al(a'	The interpreter should process the valid sequences and either ignore the invalid or return an appropriate error message.
Extremely long goal string to test performance (e.g., 10^5 characters)	The solution should scale linearly with the length of the input string to avoid timeouts; using string concatenation directly is inefficient, a string builder/buffer should be used.
Goal string containing nested or overlapping parentheses, e.g., '(()al)' or '(al)(al)'	The problem description implies simple sequential parsing, so the solution should handle overlapping parenthesis in sequential manner from left to right.

Null or empty goal string

How to Handle:

Return an empty string immediately, as there is nothing to parse.

Goal string contains only 'G'

How to Handle:

The interpreter should return 'G' itself, as there are no parentheses to interpret.

Goal string contains only '()'

How to Handle:

The interpreter should return 'o' repeated for each '()'.

Goal string contains only '(al)'

How to Handle:

The interpreter should return 'al' repeated for each '(al)'.

Goal string starts or ends with an incomplete sequence like '(' or '(a'

How to Handle:

The interpreter should ignore or return an error string depending on requirements; a robust implementation might throw an exception or log an error and continue.

Goal string with mixed valid and invalid sequences, e.g., 'G()al(a'

How to Handle:

The interpreter should process the valid sequences and either ignore the invalid or return an appropriate error message.

Extremely long goal string to test performance (e.g., 10^5 characters)

How to Handle:

The solution should scale linearly with the length of the input string to avoid timeouts; using string concatenation directly is inefficient, a string builder/buffer should be used.

Goal string containing nested or overlapping parentheses, e.g., '(()al)' or '(al)(al)'

How to Handle:

The problem description implies simple sequential parsing, so the solution should handle overlapping parenthesis in sequential manner from left to right.

Solution

Clarifying Questions

When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:

What characters will the input string `command` contain besides 'G', '()', and '(al)'?
Is the input string `command` guaranteed to be a valid sequence of the given interpretations, or could it contain invalid sequences?
Can the input string `command` be empty or null?
Is the case of the input string `command` significant? (e.g., should 'g' be treated the same as 'G')
What is the maximum possible length of the input string `command`?

Brute Force Solution

Approach

We need to translate a coded message. The brute force method simply goes through the message character by character, checking for specific patterns.

Here's how the algorithm would work step-by-step:

Look at the first character in the message.
If it's a 'G', we know it means 'G'.
If it's a '(', we need to look at the next character to see if it's part of '(al)' or '()'.
If it's followed by a ')', then the '()' pattern translates to 'o'.
If it's followed by 'al)', then the '(al)' pattern translates to 'al'.
Continue this process, character by character, replacing each pattern with its translation until we reach the end of the message.

Code Implementation

def interpret_goal_parser(command):    interpreted_string = ""    index = 0
    while index < len(command):
        # If we see a 'G', just add it to the result. 
        if command[index] == 'G':
            interpreted_string += 'G'
            index += 1
        elif command[index] == '(':            # Check if it's '()' or '(al)' 
            if command[index + 1] == ')':
                interpreted_string += 'o'
                index += 2
            else:
                # Handle the '(al)' case. 
                interpreted_string += 'al'
                index += 4
        
        else:
            index += 1

    return interpreted_string

Big(O) Analysis

Time Complexity

Space Complexity

Optimal Solution

Approach

Here's how the algorithm would work step-by-step:

Start at the beginning of the command string.
Read one character at a time.
If you see a 'G', directly add 'G' to your result.
If you see '()', directly add 'o' to your result.
If you see '(al)', directly add 'al' to your result.
Continue until you reach the end of the command string. The translated string will be complete.

Code Implementation

def interpret_goal_parser(command): 
    interpreted_string = ""
    index = 0
    command_length = len(command)

    while index < command_length:
        # Check for 'G' to add 'G' to output.
        if command[index] == 'G':
            interpreted_string += 'G'
            index += 1

        # Check for '()' to add 'o' to output.
        elif command[index] == '(' and command[index + 1] == ')':
            interpreted_string += 'o'
            index += 2

        #The remaining option must be (al) so we add "al" to the output
        else:
            interpreted_string += 'al'
            index += 4

    return interpreted_string

Big(O) Analysis

Time Complexity

Space Complexity

Edge Cases

Case	How to Handle
Null or empty goal string	Return an empty string immediately, as there is nothing to parse.
Goal string contains only 'G'	The interpreter should return 'G' itself, as there are no parentheses to interpret.
Goal string contains only '()'	The interpreter should return 'o' repeated for each '()'.
Goal string contains only '(al)'	The interpreter should return 'al' repeated for each '(al)'.
Goal string starts or ends with an incomplete sequence like '(' or '(a'	The interpreter should ignore or return an error string depending on requirements; a robust implementation might throw an exception or log an error and continue.
Goal string with mixed valid and invalid sequences, e.g., 'G()al(a'	The interpreter should process the valid sequences and either ignore the invalid or return an appropriate error message.
Extremely long goal string to test performance (e.g., 10^5 characters)	The solution should scale linearly with the length of the input string to avoid timeouts; using string concatenation directly is inefficient, a string builder/buffer should be used.
Goal string containing nested or overlapping parentheses, e.g., '(()al)' or '(al)(al)'	The problem description implies simple sequential parsing, so the solution should handle overlapping parenthesis in sequential manner from left to right.

Null or empty goal string

How to Handle:

Return an empty string immediately, as there is nothing to parse.

Goal string contains only 'G'

How to Handle:

The interpreter should return 'G' itself, as there are no parentheses to interpret.

Goal string contains only '()'

How to Handle:

The interpreter should return 'o' repeated for each '()'.

Goal string contains only '(al)'

How to Handle:

The interpreter should return 'al' repeated for each '(al)'.

Goal string starts or ends with an incomplete sequence like '(' or '(a'

How to Handle:

The interpreter should ignore or return an error string depending on requirements; a robust implementation might throw an exception or log an error and continue.

Goal string with mixed valid and invalid sequences, e.g., 'G()al(a'

How to Handle:

The interpreter should process the valid sequences and either ignore the invalid or return an appropriate error message.

Extremely long goal string to test performance (e.g., 10^5 characters)

How to Handle:

The solution should scale linearly with the length of the input string to avoid timeouts; using string concatenation directly is inefficient, a string builder/buffer should be used.

Goal string containing nested or overlapping parentheses, e.g., '(()al)' or '(al)(al)'

How to Handle:

The problem description implies simple sequential parsing, so the solution should handle overlapping parenthesis in sequential manner from left to right.