力扣第94题-二叉树的中序遍历

题目
题目链接
写个简单的爽爽

题解

/**
 * 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;
 *     }
 * }
 */
import java.util.ArrayList;
import java.util.List;

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        recursion(res, root);
        return res;
    }
    private void recursion(List<Integer> res, TreeNode node) {
        if (node == null) {
            return;
        }
        if (node.left != null) {
            recursion(res, node.left);
        }
        res.add(node.val);
        if (node.right != null) {
            recursion(res, node.right);
        }
    }
}