Difficulty: Medium
Given a binary tree, return the inorder traversal of its nodes' values.
Example:
Input: [1,null,2,3]
1
\
2
/
3
Output: [1,3,2]
Follow up: Recursive solution is trivial, could you do it iteratively?
Language: Java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<Integer> inorderTraversal(TreeNode root) {
Stack<TreeNode> stack = new Stack<>();
List<Integer> result = new ArrayList<>();
TreeNode p = root;
while (p != null || !stack.isEmpty()) {
// 一直向左，把所有节点压栈
while (p != null) {
stack.push(p);
p = p.left;
}
// 压栈结束，元素出栈
p = stack.pop();
// 打印 value
result.add(p.val);
// 对右子树做同样的操作
p = p.right;
}
return result;
}
}