很浪漫的代码：大胆地往前走，我们都是对方的退路。

class Solution:
    def FindFirstCommonNode(self , pHead1 , pHead2 ):
        # write code here
        mark1,mark2=pHead1,pHead2
        while mark1!=mark2:
            mark1=mark1.next if mark1 else pHead2
            mark2=mark2.next if mark2 else pHead1
        else:
            return mark1
        return None