【leetcode】722. Remove Comments

题目如下：

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  .

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
line
more_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.

解题思路：这种题目还是很烦的，要考虑的情况比较多。我的方法相对简单粗暴一点，首先设置一个定界符，例如：'#$%@'。然后把所有的换行符都替换成定界符，这样相当于把代码都合并到一行。接下来查找下标最小的'//'和'/*'，如果'/*'的下标更小找出在后面最近的'*/'，删除掉之间所有字符；否则，找出'//'后面最近的定界符，并且删除到之间的所有字符。循环操作直到所有合法的//'和'/*'都删除掉为止，最后把定界符再替换回换行符。

代码如下：

class Solution(object):
    def removeComments(self, source):
        """
        :type source: List[str]
        :rtype: List[str]
        """
        newLine = ''
        delimiter = '#$%@'
        for i in source:
            newLine += i
            newLine += delimiter

        while True:
            linecommentStart = newLine.find('//')
            blockCommentStart  = newLine.find('/*')
            if linecommentStart == -1 and blockCommentStart == -1:
                break
            elif linecommentStart == -1:
                blockCommentEnd = newLine.find('*/',blockCommentStart+2)
                if blockCommentEnd == -1:
                    break
                newLine = newLine[:blockCommentStart] + newLine[blockCommentEnd+2:]
            elif blockCommentStart == -1:
                linecommentEnd = newLine.find(delimiter,linecommentStart)
                newLine = newLine[:linecommentStart] + newLine[linecommentEnd + 4:]
            else:
                if linecommentStart < blockCommentStart:
                    linecommentEnd = newLine.find(delimiter, linecommentStart)
                    newLine = newLine[:linecommentStart] + newLine[linecommentEnd:]
                else:
                    blockCommentEnd = newLine.find('*/', blockCommentStart + 2)
                    if blockCommentEnd != -1:
                        newLine = newLine[:blockCommentStart] + newLine[blockCommentEnd + 2:]
                    else:
                        linecommentEnd = newLine.find(delimiter, linecommentStart)
                        newLine = newLine[:linecommentStart] + newLine[linecommentEnd:]
        def filterEmpty(n):
            return len(n) > 0

        return list(filter(filterEmpty, newLine.split(delimiter)))