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Remove Comments

Given a C++ program, remove comments from it. The program source is an array of strings source where source[i] is the ith line of the source code. This represents the result of splitting the original source code string by the newline character '\n'.

In C++, there are two types of comments, line comments, and block comments.

  • The string "//" denotes a line comment, which represents that it and the rest of the characters to the right of it in the same line should be ignored.
  • The string "/*" denotes a block comment, which represents that all characters until the next (non-overlapping) occurrence of "*/" should be ignored. (Here, occurrences happen in reading order: line by line from left to right.) To be clear, the string "/*/" does not yet end the block comment, as the ending would be overlapping the beginning.

The first effective comment takes precedence over others.

  • For example, if the string "//" occurs in a block comment, it is ignored.
  • Similarly, if the string "/*" occurs in a line or block comment, it is also ignored.

If a certain line of code is empty after removing comments, you must not output that line: each string in the answer list will be non-empty.

There will be no control characters, single quote, or double quote characters.

  • For example, source = "string s = "/* Not a comment. */";" will not be a test case.

Also, nothing else such as defines or macros will interfere with the comments.

It is guaranteed that every open block comment will eventually be closed, so "/*" outside of a line or block comment always starts a new comment.

Finally, implicit newline characters can be deleted by block comments. Please see the examples below for details.

After removing the comments from the source code, return the source code in the same format.

 

Example 1:

Input: source = ["/*Test program */", "int main()", "{ ", "  // variable declaration ", "int a, b, c;", "/* This is a test", "   multiline  ", "   comment for ", "   testing */", "a = b + c;", "}"]
Output: ["int main()","{ ","  ","int a, b, c;","a = b + c;","}"]
Explanation: The line by line code is visualized as below:
/*Test program */
int main()
{ 
  // variable declaration 
int a, b, c;
/* This is a test
   multiline  
   comment for 
   testing */
a = b + c;
}
The string /* denotes a block comment, including line 1 and lines 6-9. The string // denotes line 4 as comments.
The line by line output code is visualized as below:
int main()
{ 
  
int a, b, c;
a = b + c;
}

Example 2:

Input: source = ["a/*comment", "line", "more_comment*/b"]
Output: ["ab"]
Explanation: The original source string is "a/*comment\nline\nmore_comment*/b", where we have bolded the newline characters.  After deletion, the implicit newline characters are deleted, leaving the string "ab", which when delimited by newline characters becomes ["ab"].

 

Constraints:

  • 1 <= source.length <= 100
  • 0 <= source[i].length <= 80
  • source[i] consists of printable ASCII characters.
  • Every open block comment is eventually closed.
  • There are no single-quote or double-quote in the input.

Solution Explanation

This problem requires removing comments from a C++ source code represented as an array of strings. There are two types of comments: line comments (//) and block comments (/* ... */). The solution involves iterating through each line and handling both comment types.

Algorithm:

  1. Initialization: Initialize an empty list ans to store the processed lines, a temporary string t (or equivalent data structure depending on language) to accumulate characters within a line before adding to ans, and a boolean variable blockComment to track whether we're inside a block comment.

  2. Line Iteration: The solution iterates through each line (s) in the input source.

  3. Character Iteration: Inside the line iteration, a nested loop iterates through each character of the line.

  4. Block Comment Handling: If blockComment is true (we are inside a block comment):

    • Check for the end of the block comment (*/). If found, set blockComment to false and skip over the */.
    • Otherwise, continue to the next character.

  5. Line and Block Comment Detection: If blockComment is false:

    • Check for the start of a line comment (//). If found, break out of the inner loop (to skip the rest of the line).
    • Check for the start of a block comment (/*). If found, set blockComment to true and skip over the /*.
    • Otherwise, append the current character to the temporary string t.

  6. Line Accumulation: After processing a line:

    • If blockComment is false and t is not empty, add the content of t to ans and clear t. This ensures that only the non-commented parts of each line are added.

  7. Return Value: Finally, return the ans list containing the processed lines.

Time Complexity: O(N*M), where N is the number of lines in the source code and M is the maximum length of a line. The solution iterates through each character of each line once.

Space Complexity: O(NM) in the worst case, where all characters except comments are added to the result. The space used is proportional to the size of the output. In most cases, space used is significantly less than O(NM) as comments often take up a significant portion of the code.

Code Examples (Python, Java, C++, Go, TypeScript and Rust):

The code examples in different programming languages demonstrate the implementation of this algorithm. Each example follows the same logic, but utilizes language-specific syntax and data structures. The crucial part is handling the blockComment flag to accurately manage nested block comments and line comments. Note that empty lines are automatically omitted because the t variable (or equivalent) is checked for emptiness before adding the line to the result.