Add_One_Row_To_Tree.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 Solution {

    public TreeNode helper(TreeNode root,int val,int depth,int currdepth){
        if(depth==1){
            TreeNode zoo=new TreeNode(val);
            zoo.left=root;
            return zoo;
        }

        if(root==null){
            return root;
        }

        if(currdepth==depth-1){
            TreeNode leftman=root.left;
            TreeNode rightman=root.right;

            root.left=new TreeNode(val);
            root.right=new TreeNode(val);

            root.left.left=leftman;
            root.right.right=rightman;
            return root;
            
        }

        helper(root.left,val,depth,currdepth+1);
        helper(root.right,val,depth,currdepth+1);

        return root;

    }
    public TreeNode addOneRow(TreeNode root, int val, int depth) {
     return  helper(root,val,depth,1);

        
    }
}