100. Same Tree

class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
      if ( p == null && q == null){
        return true;
      }else if (p == null || q == null){
        return false;
      }else{
        return (p.val == q.val) && isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
      }
    }
}