面试题52：两个链表的第一个公共节点

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def FindFirstCommonNode(self, pHead1, pHead2):
        # write code here
        #参数1：较短的链表
        #参数2：较长的链表
        #参数3：较短的链表头
        #参数4：较长的链表头
        def findequal(shortpointer,longpointer,shortHead,longHead):
            #temp1没遍历完，也就是没走到头
            k = 0
            while longpointer:
                longpointer = longpointer.next
                k += 1
            longpointer = longHead
            shortpointer = shortHead
            for i in range(k):
                longpointer = longpointer.next
            while  longpointer != shortpointer:
                longpointer = longpointer.next
                shortpointer = shortpointer.next
            return shortpointer
        
        # 2个链表呈现Y字形，让2个链表从头到尾开始遍历
        temp1 = pHead1
        temp2 = pHead2
        while temp1 and temp2:
            if temp1 == temp2:
                return temp1
            temp1 = temp1.next
            temp2 = temp2.next
        
        if temp1:
            #temp1没遍历完，也就是没走到头
            #findequal(shortpointer,longpointer,shortHead,longHead)
            return findequal(temp2,temp1,pHead2,pHead1)
            """
            k = 0
            while temp1:
                temp1 = temp1.next
                k += 1
            temp1 = pHead1
            temp2 = pHead2
            for i in range(k):
                temp1 = temp1.next
            while  temp1 != temp2:
                temp1 = temp1.next
                temp2 = temp2.next
            return temp1
            """
        if temp2:
            #temp2没遍历完，也就是没走到头
            return findequal(temp1,temp2,pHead1,pHead2)
            """
            k = 0
            while temp2:
                temp2 = temp2.next
                k += 1
            temp1 = pHead1
            temp2 = pHead2
            for i in range(k):
                temp2 = temp2.next
            while temp1 != temp2:
                temp1 = temp1.next
                temp2 = temp2.next
            return temp1
            """