剑指offer----两个链表的第一个公共节点

#defination of ListNode
class ListNode:
    def __init__(self,x):
        self.val=x
        self.next=None

class solution:
    def firstComment(self,head1,head2):
        temp1,temp2=head1,head2
        while temp1.next is not None and temp2.next is not None:
            temp1=temp1.next
            temp2=temp2.next
            if temp1==temp2:
                return temp1.val
        if temp1.next is None:
            temp1,temp2=temp2,head1
        elif temp2.next is None:
            temp1,temp2=head2,temp1
        while temp1 is not None:
            if temp1==temp2:
                return temp1.val
            temp1=temp1.next
            temp2=temp2.next
if __name__=="__main__":
    head1=ListNode(1)
    head1.next=ListNode(2)
    head2=ListNode(3)
    head1.next.next=head2.next=ListNode(4)
    su=solution()
    print(su.firstComment(head1,head2))