722. Remove Comments

Description

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.

Problem URL

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Solution

给一个String[] 表示的程序文本，去除里面“//”和“/**/”形式的注释。

Use a Array list to stroe result, and a string builder to get new string with less resource(or string = “” is ok). A boolean multi is for multiple lines comment.

For every string in source, for every character in this string. If we are in a multi lines comment, judge if we could jump out, when jump out, use I++ for jump two characters(out of “*/”). If we are not in a multi lines comment, there are three circumstances.

1. normal code, append it to stringbuilder.
2. “//”, just ignore this string ,that is break.
3. “/*” multi is true, jump to I++ posion.

After a string’s iteration is complete, if we are not in multi and string builder has characters, add it to res. Then new a new string builder.

Code

class Solution {
    public List<String> removeComments(String[] source) {
        StringBuilder sb = new StringBuilder();
        List<String> res = new ArrayList<>();
        boolean multi = false;
        for (String s : source){
            for (int i = 0; i < s.length(); i++){
                if (multi){
                    if (s.charAt(i) == '*' && i < s.length() - 1 && s.charAt(i+1) == '/'){
                        multi = false;
                        i++;
                    }
                }
                else{
                    if (s.charAt(i) == '/' && i < s.length() - 1 && s.charAt(i+1) == '/'){
                        break;
                    }
                    if (s.charAt(i) == '/' && i < s.length() - 1 && s.charAt(i+1) == '*'){
                        multi = true;
                        i++;
                    }
                    else{
                        sb.append(s.charAt(i));
                    }
                }
            }
            if (!multi && sb.length() > 0){
                res.add(sb.toString());
                sb = new StringBuilder();
            }
        }
        return res;
    }
}

Time Complexity: O(m * n)
Space Complexity: O(m * n)

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Review

String builder would cost less resources than new a string every time.