Leetcode 之Populating Next Right Pointers in Each Node II（51）

void connect(TreeLinkNode *root)
      {
          while (root)
          {
              //每一层循环时重新初始化
              TreeLinkNode *prev = nullptr;
              TreeLinkNode *next = nullptr;
              //对于每一层
              for (; root; root = root->next)
              {
                  //每一层开始时，记录下一层的起始结点
                  if (!next)next = root->left ? root->left : root->right;

                  if (root->left)
                  {
                      //如果不是起始结点，则将prev与该左子结点相连接
                      if (prev)prev->next = root->left;
                      //如果是每层的起始结点，则将左子结点直接赋给prev
                      prev = root->left;
                  }
                  if (root->right)
                  {
                      if (prev)prev->next = root->right;
                      prev = root->right;
                  }
              }
              root = next;
          }
      }