/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Pair{
    TreeNode x;
    TreeNode y;
    public Pair(TreeNode x, TreeNode y){
        this.x = x;
        this.y = y;
    }
}
public class Solution {
    //recursive
    // public boolean isSameTree(TreeNode p, TreeNode q) {
    //     if(p == null && q == null)
    //         return true;
    //     if(p == null || q== null || p.val != q.val)
    //         return false;
    //     return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    // }
    
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p == null && q == null)
            return true;
        if(p == null || q== null || p.val != q.val)
            return false;
        Queue<Pair> queue = new LinkedList<Pair>();
        queue.offer(new Pair(p, q));
        while(!queue.isEmpty()){
            Pair values = queue.poll();
            if(values.x  == null && values.y == null)
                continue;
            if(values.x != null && values.y != null){
                queue.offer(new Pair(values.x.left, values.y.left));
                queue.offer(new Pair(values.x.right, values.y.right));
            }
            if(values.x == null || values.y == null || values.x.val != values.y.val) return false;
        }
        return true;
    }
}