c++ - 两个带有 STL 迭代器的循环

Question

我如何使用 STL 迭代器重写这个？

for (int i = 0; i < board.size(); i++) {
      for (int j = 0; j < board[i].size(); j++) {
        if (board[i][j] == '*') {
          if (board[i][j + 1] == '*') {
            j++;
            sum += a;
          } else {
            sum += b;
          }
        }
      }
    }

我必须看到这样的东西(但也许这不是个好主意？):

vector<string>::iterator board_elem;
vector<string>::iterator cell_itr;

for (board_elem = board.begin(); board_elem != board.end(); board_elem++) {
  for (cell_itr = board_elem.begin(); cell_itr != board_elem.end(); cell_itr++) {
    cout << board_elem[cell_itr];
  }
}

Answer 1

一般来说，我看不出为什么你应该在这里使用迭代器，但如果你想:

for (auto bit = board.begin(); bit != board.end(); ++bit) {
    for (auto sit = bit->begin(); sit < bit->end(); ++sit) {
        if (*sit == '*') {
            if (*(++sit) == '*') {
                sum += a;
            } else {
                sum += b;
            }
        }
    }
}

如果您不能保证最后一个字符不是 '*'，那么您必须将最后一个 if 替换为以下内容:

if ((cit+1) != it->end()  && *(++cit) == '*') { 

如果你喜欢 hack 一点，你也可以使用基于范围的 for 循环(虽然我不推荐它):

for (auto& e : board) {
    bool isFirst=true; //next * will be the first one in a row
    for (auto& c : e) {
        if (c == '*') {         
            sum += b;
            if (!isFirst) {
                sum = sum - 2*b + a; //second in a row - subtract what we falsely added             
            }   
            isFirst=!isFirst;           
        } else {
            isFirst = true;
        }
    }
}