func FindFirstCommonNode( pHead1 *ListNode ,  pHead2 *ListNode ) *ListNode {
    // write code here
    var answer *ListNode
    head1 := pHead1
    head2 := pHead2
    for head1 != nil {
        head2=pHead2
        for head2 != nil {
            if head1.Val==head2.Val {
                answer = head1
                return answer
            }
            head2 = head2.Next
        }
        head1 = head1.Next
    }
    return answer
}