remove-comments.py

# Time:  O(n), n is the length of the source
# Space: O(k), k is the max length of a line

# Given a C++ program, remove comments from it.
# The program source is an array where source[i] is the i-th 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
# 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:
# 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;", "}"]
#
# 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;
# }
#
# Output: ["int main()","{ ","  ","int a, b, c;","a = b + c;","}"]
#
# The line by line code is visualized as below:
# int main()
# { 
# int a, b, c;
# a = b + c;
# }
# Explanation: 
# The string 
# /*
#  denotes a block comment, including line 1 and lines 6-9. The string 
# //
#  denotes line 4 as comments.
#
# 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"].
#
# Note:
# - The length of source is in the range [1, 100].
# - The length of source[i] is in the range [0, 80].
# - Every open block comment is eventually closed.
# - There are no single-quote, double-quote, or control characters in the source code.

class Solution(object):
    def removeComments(self, source):
        """
        :type source: List[str]
        :rtype: List[str]
        """
        in_block = False
        result, newline = [], []
        for line in source:
            i = 0
            while i < len(line):
                if not in_block and i+1 < len(line) and line[i:i+2] == '/*':
                    in_block = True
                    i += 1
                elif in_block and i+1 < len(line) and line[i:i+2] == '*/':
                    in_block = False
                    i += 1
                elif not in_block and i+1 < len(line) and line[i:i+2] == '//':
                    break
                elif not in_block:
                    newline.append(line[i])
                i += 1
            if newline and not in_block:
                result.append("".join(newline))
                newline = []
        return result