给定一个二叉树,返回它的中序遍历。
示例:
输入: [1,null,2,3]
输出: [1,3,2]
中序遍历:
中序遍历首先遍历左子树,然后访问根结点,最后遍历右子树。若二叉树为空则结束返回。
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) {
List<Integer> list = new ArrayList<>();
Stack<TreeNode> stack = new Stack<>();
while(root != null || !stack.isEmpty()){
while(root != null){
stack.push(root);
root = root.left;
}
root = stack.pop();
list.add(root.val);
root = root.right;
}
return list;
}
}