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• Java
• C++
• Python

• import java.util.ArrayList;
  import java.util.List;
  import java.util.regex.Pattern;
  
  /**
  
   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.
  
   */
  
  public class Remove_Comments {
  
      public static void main(String[] args) {
          Remove_Comments out = new Remove_Comments();
          Solution s = out.new Solution();
  
  //        String[] input = new String[]{"int main()","{ ","  ","int a, b, c;","a = b + c;","}"};
  //
  //        System.out.println(s.removeComments(input));
  //
  //        System.out.println(s.removeComments_ac(input));
  
  
          String[] input2 = new String[]{"/*Test program */", "int main()", "{ ", "  // variable declaration ", "int a, b, c;", "/* This is a test", "   multiline  ", "   comment for ", "   testing */", "a = b + c;", "}"};
  
          System.out.println(s.removeComments(input2));
          System.out.println(s.removeComments_ac(input2));
      }
  
      class Solution {
          public List<String> removeComments(String[] source) {
  
              List<String> result = new ArrayList<>();
  
              if (source == null || source.length == 0) {
                  return result;
              }
  
              boolean unclosed = false;
              Pattern line = Pattern.compile("\\/\\/");
              Pattern blockStart = Pattern.compile("\\/\\*");
              Pattern blockEnd = Pattern.compile("\\*\\/");
  
              for (String each: source) {
                  if (unclosed) { // failed by "/*Test program */", find "/*" and it's always unclosed
                      continue;
                  } else if (line.matcher(each).find()) {
                      continue;
                  } else if (blockStart.matcher(each).find()) {
                      unclosed = true;
                  } else if (blockEnd.matcher(each).find()) {
                      unclosed = false;
                  } else {
                      result.add(each);
                  }
              }
  
              return result;
          }
  
          public List<String> removeComments_ac(String[] source) {
              List<String> result = new ArrayList();
  
              if (source == null || source.length == 0) {
                  return result;
              }
  
              boolean unclosed = false;
              StringBuilder newline = new StringBuilder();
  
              for (String line: source) {
                  int i = 0;
                  char[] chars = line.toCharArray();
                  if (!unclosed) newline = new StringBuilder();
  
                  // scan through this line
                  while (i < line.length()) {
                      if (!unclosed && i+1 < line.length() && chars[i] == '/' && chars[i+1] == '*') {
                          unclosed = true;
                          i++;
                      } else if (unclosed && i+1 < line.length() && chars[i] == '*' && chars[i+1] == '/') {
                          unclosed = false;
                          i++;
                      } else if (!unclosed && i+1 < line.length() && chars[i] == '/' && chars[i+1] == '/') {
                          break;
                      } else if (!unclosed) {
                          newline.append(chars[i]);
                      }
  
                      i++;
                  }
  
                  if (!unclosed && newline.length() > 0) {
                      result.add(new String(newline));
                  }
              }
  
              return result;
          }
  
      }
  
  }
  

• // OJ: https://leetcode.com/problems/remove-comments/
  // Time: O(N)
  // Space: O(1) excluding the space taken by the answer
  class Solution {
      bool match(string &s, int start, string target) {
          return start + 2 <= s.size() && s[start] == target[0] && s[start + 1] == target[1];
      }
  public:
      vector<string> removeComments(vector<string>& A) {
          vector<string> ans;
          bool block = false;
          for (int i = 0, N = A.size(); i < N; ++i) {
              int j = 0;
              if (!block) ans.emplace_back();
              while (j < A[i].size()) {
                  if (block) {
                      if (match(A[i], j, "*/")) {
                          block = false;
                          j += 2;
                      } else ++j;
                  } else if (match(A[i], j, "/*")) {
                      block = true;
                      j += 2;
                  } else if (match(A[i], j, "//")) {
                      break;
                  } else {
                      ans.back() += A[i][j++];
                  }
              } 
              if (ans.back().empty()) ans.pop_back();
          }
          return ans;
      }
  };
  

• class Solution(object):
      def removeComments(self, source):
          """
          :type source: List[str]
          :rtype: List[str]
          """
          res = []
          multi = False
          line = ''
          for s in source:
              i = 0
              while i < len(s):
                  if not multi:
                      if s[i] == '/' and i < len(s) - 1 and s[i + 1] == '/':
                          break
                      elif s[i] == '/' and i < len(s) - 1 and s[i + 1] == '*':
                          multi = True
                          i += 1
                      else:
                          line += s[i]
                  else:
                      if s[i] == '*' and i < len(s) - 1 and s[i + 1] == '/':
                          multi = False
                          i += 1
                  i += 1
              if not multi and line:
                  res.append(line)
                  line = '' # 注意line重新设置成空字符串的位置
          return res
  
  

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