文本左右对齐

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class Solution {
 public:
  vector<string> fullJustify(vector<string>& words, int maxWidth) {
    vector<string> res;
    for (int i = 0; i < words.size(); i++) {
      int j = i + 1;
      int len = words[i].size();
      // 数一数可以把后面多少个单词加到当前行
      while (j < words.size() && len + 1 + words[j].size() <= maxWidth)
        len += 1 + words[j++].size();

      string line;
      if (j == words.size() || j == i + 1) {
        // 如果是最后一行
        line += words[i];
        for (int k = i + 1; k < j; k++) {
          line += ' ' + words[k];
        }
        while (line.size() < maxWidth) line += ' ';
      } else {
        // cnt 是空隙的数量，j 指向最后一个加入当前行单词的下一个单词，i 指向当前枚举的单词
        int cnt = j - i - 1, r = maxWidth - len + cnt;
        line += words[i];
        int k = 0;
        while (k < r % cnt)
          line += string(r / cnt + 1, ' ') + words[i + k + 1], k++;
        while (k < cnt) line += string(r / cnt, ' ') + words[i + k + 1], k++;
      }
      res.push_back(line);
      i = j - 1;
    }
    return res;
  }
};