Loop Binary Tree Solution - Binary Tree Level Order Traversal

The idea is to define a queue to process level by level. A variable levelSize is used to mark each level and load to that level result list.  Update the levelSize to be the queue size when reach zero.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
        if(root == null){
            return new ArrayList<ArrayList<Integer>>();
        }
        Queue<TreeNode> process = new LinkedList<TreeNode>();
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> midResult = new ArrayList<Integer>();
        process.offer(root);
        int levelCount = process.size();;
        while(!process.isEmpty()){
            TreeNode cur = process.poll();
            midResult.add(cur.val);
            levelCount--;
            if(cur.left != null){
                process.offer(cur.left);
            }
            if(cur.right != null){
                process.offer(cur.right);
            }
            if(levelCount == 0){
                result.add(midResult);
                midResult = new ArrayList<Integer>();
                levelCount = process.size();
            }
        }
        return result;
    }
}