Day-9 Maximum Width of Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int widthOfBinaryTree(TreeNode root) {
        if (root == null)
            return 0;
        LinkedList<Pair<TreeNode, Integer>> queue = new LinkedList<>();
        Integer maxWidth = 0;

        queue.addLast(new Pair<>(root, 0));
        while (queue.size() > 0) {
            Pair<TreeNode, Integer> head = queue.getFirst();
            Integer currLevelSize = queue.size();
            Pair<TreeNode, Integer> elem = null;
            for (int i = 0; i < currLevelSize; ++i) {
                elem = queue.removeFirst();
                TreeNode node = elem.getKey();
                if (node.left != null)
                    queue.addLast(new Pair<>(node.left, 2 * elem.getValue()));
                if (node.right != null)
                    queue.addLast(new Pair<>(node.right, 2 * elem.getValue() + 1));
            }
            maxWidth = Math.max(maxWidth, elem.getValue() - head.getValue() + 1);
        }

        return maxWidth;
    }
}

class Solution {
    int max=1;
    public int widthOfBinaryTree(TreeNode root) {
        List<Integer> start=new ArrayList<>();
        helper(root,0,1,start);
        return max;    
    }
    
    void helper(TreeNode node,int level,int index,List<Integer> start){
        if(node==null) return;
        if(level==start.size()) start.add(index);
        max=Math.max(max,index+1-start.get(level));
        helper(node.left,level+1,2*index,start);
        helper(node.right,level+1,2*index+1,start);
    }
    
    
}