Checking if two binary trees are identical
Your code already does its job well. It can be shortened a bit:

public boolean isSameTree(TreeNode p, TreeNode q) {
    if (p == null || q == null) {
        return p == q;
    }

    return p.val == q.val
        &amp;&amp; isSameTree(p.left, q.left)
        &amp;&amp; isSameTree(p.right, q.right);
}


I flipped the operands of the == operators since having null in the right hand side reads more naturally.

I added spaces after the if and after the commas to follow the common formatting style.