Thinking:

  • Method:
    • 中序遍历
    • 左 -> 中 -> 右
/**
 * 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> result = new ArrayList<>();
        if(root == null) return result;
        inorder(root, result);
        return result;
    }
    private static void inorder(TreeNode n, List<Integer> result){
        if(n == null) return;
        inorder(n.left, result);
        result.add(n.val);
        inorder(n.right, result);
    }
}

二刷

前序，中序， 后续遍历是指父节点在两个子节点之间的位置的。这种题目必须无压力几分钟写出来。

/**
 * 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> result = new LinkedList<>();
        inorderTraversal(result, root);
        return result;
    }
    private void inorderTraversal(List<Integer> result, TreeNode root){
        if(root == null) return;
        inorderTraversal(result, root.left);
        result.add(root.val);
        inorderTraversal(result, root.right);
    }
}