Binary Tree Inorder Traversal

二叉树中序遍历迭代法

最新推荐文章于 2022-03-31 17:31:26 发布

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本文介绍了一种不使用递归实现二叉树中序遍历的方法，通过迭代方式利用栈来存储节点，直到达到最左下节点开始访问，并返回节点值列表。

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

For example:
Given binary tree {1,#,2,3},

return [1,3,2].

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

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

思路： iterative，利用stack 来存储左边节点，直到到达最左最下开始访问，访问完就向右边走，否则取栈顶元素

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> ret = new ArrayList<Integer>();
        if(root == null)
            return ret;
        Stack<TreeNode> s = new Stack<TreeNode>();
        TreeNode cur = root;
        while(cur != null || !s.isEmpty()){
            while(cur != null){
                s.push(cur);
                cur = cur.left;
            }
            cur = s.pop();
            ret.add(cur.val);
            cur = cur.right;
        }
        return ret;
    }
}