94. Binary Tree Inorder Traversal

1. Question

Given the root of a binary tree, return the inorder traversal of its nodes' values.

2. Examples

Example 1:

Input: root = [1,null,2,3]
Output: [1,3,2]

Example 2:

Input: root = []
Output: []

Example 3:

Input: root = [1]
Output: [1]

Example 4:

Input: root = [1,2]
Output: [2,1]

Example 5:

Input: root = [1,null,2]
Output: [1,2]

3. Constraints

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100

Follow up: Recursive solution is trivial, could you do it iteratively?

4. References

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/binary-tree-inorder-traversal 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

5. Solutions

class Solution {
    List<Integer> list = new ArrayList<>();

    public List<Integer> inorderTraversal(TreeNode root) {
        sort(root);
        return list;
    }

    public void sort(TreeNode root) {
        if (root == null) {
            return;
        }
        sort(root.left);
        list.add(root.val);
        sort(root.right);
    }
}