目录

leetcode-hot-100-94二叉树的中序遍历

JAY.LIN 收录于未分类

2025-03-14 约 274 字预计阅读 1 分钟

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目录

【leetcode hot 100 94】二叉树的中序遍历

错误解法一：只用一个函数进行递归。当 `root==null` 时，返回的是 `null` ，而不是 `list` ！！！！

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

解法一：递归

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        inorder(root, list);
        return list;
    }

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

注意：

申请list要放在外面，否则返回null，并不是list！！！！