leetcode https://leetcode.com/problems/binary-tree-inorder-traversal/ Java Solution

BinaryTree_inorderTraversal.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> arr = new ArrayList<>();
        if(root == null){
            return arr;
        }
        TreeNode current = root;
        List<TreeNode> nodeList = new ArrayList<>();
        nodeList.add(current);
        while(!nodeList.isEmpty()){
            while(current.left != null){
                nodeList.add(current.left);
                current = current.left;
            }
            TreeNode left = nodeList.remove(nodeList.size() -1 );
            arr.add(left.val);
            TreeNode right = left.right;
            if(right != null){
                current  = right;
                nodeList.add(right);
            }
        }
        return arr;
    }
}