[leetcode] 94. Binary Tree Inorder Traversal

原题

思路：
Dfs.

class Solution {
 public:
  vector<int> inorderTraversal(TreeNode *root) {
    vector<int> vec;
    dfs(root, vec);
    return vec;
  }
  void dfs(TreeNode *root, vector<int> &vec) {
    if (root) {
      dfs(root->left, vec);
      vec.push_back(root->val);
      dfs(root->right, vec);
    }
  }
};