Leecode打卡第二十一天

Leecode打卡第二十一天

二叉树的中序遍历

给定一个二叉树的根节点 root ，返回 它的 中序 遍历 。

主要思想：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> res = new ArrayList<>();
        indorder(root, res);
        return res;
    }
    void indorder(TreeNode root, List<Integer> list){
        if(root == null) return;
        indorder(root.left, list);
        list.add(root.val);
        indorder(root.right, list);
    }
}