Leetcode 之Binary Tree Inorder Traversal（43）

vector<int> inorderTraversal(TreeNode *root)
      {
          vector<int> result;
          stack<TreeNode *>s;
          TreeNode *p = root;
          while (!s.empty() || p != nullptr)
          {
              if (p != nullptr)
              {
                  //将当前结点和其左结点不断入栈
                  s.push(p);
                  p = p->left;
              }
              else
              {
                  //访问到了左结点末尾
                  //访问该结点并弹出
                  p = s.top();
                  result.push_back(p->val);
                  s.pop();
                  //将方向转为其右结点
                  p = p->right;
              }
          }
          return result;
      }