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Remove Comments

Difficulty: Medium

Problem Description

Given a C++ program, remove comments from it. The program source is an array of strings where each string represents a line of the source code. In C++, there are two types of comments: line comments (starting with "//") and block comments (starting with "/" and ending with "/"). The goal is to return the source code without comments, ensuring that each string in the output list is non-empty.

Key Insights

  • Line comments ignore everything to the right on the same line.
  • Block comments ignore everything between "/" and "/", including across multiple lines.
  • Comments can overlap, but only the first effective comment type is considered.
  • Lines that become empty after removing comments should be excluded from the output.

Space and Time Complexity

Time Complexity: O(n * m) where n is the number of lines and m is the average length of each line, since we may need to scan each character of every line. Space Complexity: O(n) for the resultant list of non-empty lines after comments are removed.

Solution

To solve the problem, we will use a straightforward approach that involves iterating through each line of the source code and processing each character to identify comments. We'll maintain a state to determine if we are inside a block comment. If we encounter a line comment or a block comment, we'll skip appending characters to our result. Finally, we'll filter out any empty lines before returning the result.

Code Solutions

def removeComments(source):
    in_block_comment = False
    result = []
    current_line = []

    for line in source:
        i = 0
        while i < len(line):
            if not in_block_comment:
                # Check for line comment
                if line[i:i+2] == "//":
                    break  # Ignore the rest of the line
                # Check for block comment
                elif line[i:i+2] == "/*":
                    in_block_comment = True
                    i += 1  # Skip next character
                else:
                    current_line.append(line[i])
            else:
                # We're in a block comment
                if line[i:i+2] == "*/":
                    in_block_comment = False
                    i += 1  # Skip next character
            i += 1
        
        if not in_block_comment and current_line:
            result.append(''.join(current_line))
            current_line = []

    return result
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