LeetCode—94. Binary Tree Inorder Traversal

LeetCode—94. Binary Tree Inorder Traversal

题目

https://leetcode.com/problems/binary-tree-inorder-traversal/description/
中序遍历二叉树。

思路及解法

写的时候还是不熟练，还要好好想想，所以不要不重视。。
1.递归
2.非递归，栈

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    List<Integer> list = new ArrayList<>();
    public List<Integer> inorderTraversal(TreeNode root) {
        inOrder(root);
        return list;
    }
    public void inOrder(TreeNode node){
        if(node==null) return;
        if(node.left!=null){
            inOrder(node.left);
        }
        list.add(node.val);
        if(node.right!=null){
            inOrder(node.right);
        }
    }
}

/**
 * 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<>();
        if (root == null) {
            return list;
        }
        Stack<TreeNode> stack = new Stack<>();
        while(root!=null || !stack.isEmpty()){
            if(root!=null){
                stack.push(root);
                root = root.left;
            }else{
                root = stack.pop();
                list.add(root.val);
                root = root.right;
            }
        }
        return list;
    }
}