InOrderTraversal.java

/**
 * 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 InOrderTraversal {
    /*
    Runtime: 0 ms, faster than 100.00% of Java online submissions for Binary Tree Inorder Traversal.
Memory Usage: 37.5 MB, less than 18.81% of Java online submissions for Binary Tree Inorder Traversal.
    */
    ArrayList<Integer> list=new ArrayList<>();
    public List<Integer> inorderTraversal(TreeNode root) {
        if(root==null) return list;
        
           inOrder(root); 
        return list;
    }
    
    public void inOrder(TreeNode root)
    {
        if(root==null)
        {
            return;
        }
        
        inOrder(root.left);
        list.add(root.val);
        inOrder(root.right);
    }
}