問題描述：

編寫一個程序，找到兩個單鏈表相交的起始節點。

例如，下面的兩個鏈表：

A:          a1 → a2
                   ↘
                     c1 → c2 → c3
                   ↗            
B:     b1 → b2 → b3

在節點 c1 開始相交。

方法1：

 1 class Solution(object):
 2     def getIntersectionNode(self, headA, headB):
 3         """
 4         :type head1, head1: ListNode
 
 5         :rtype: ListNode
 6         """
 7         if not headA or not headB:
 8             return None
 9         p = headA
10         q = headB
11         while p and q:
12             if p.val == q.val:
13                 
14                 return p
15             elif p.val < q.val:
16                 p = p.next
 
17             else:
18                 q = q.next
19         return None

官方:求出兩個表的長度，表長的先走一個差值。

 1 class Solution(object):
 2     def getIntersectionNode(self, headA, headB):
 3         """
 4         :type head1, head1: ListNode
 5         :rtype: ListNode
 6         """
 7         lenA = 0
 8         headA_c1 = headA
 
 9         while headA_c1:
10             lenA += 1
11             headA_c1 = headA_c1.next
12         lenB = 0
13         headB_c1 = headB
14         while headB_c1:
15             lenB += 1
16             headB_c1 = headB_c1.next
17         headA_c2 = headA
18         headB_c2 = headB
19         if lenA > lenB:
20             for i in range(lenA-lenB):
21                 headA_c2 = headA_c2.next
22         elif lenA < lenB:
23             for i in range(lenB-lenA):
24                 headB_c2 = headB_c2.next
25         while headA_c2 and headB_c2:
26             if headA_c2 == headB_c2:
27                 return headA_c2
28             headB_c2 = headB_c2.next
29             headA_c2 = headA_c2.next
30         return None

方法3：

 1 class Solution(object):
 2     def getIntersectionNode(self, headA, headB):
 3         """
 4         :type head1, head1: ListNode
 5         :rtype: ListNode
 6         """
 7         temp = set()        
 8         tempA = headA
 9         tempB = headB
10         
11         if headA and headB is None:
12             return None
13         
14         while tempA:
15             temp.add(tempA)
16             tempA = tempA.next
17             
18         while tempB:
19             if tempB in temp:
20                 return tempB
21             tempB = tempB.next
22         
23         return None

2018-09-14 16:26:48

LeetCode--160--相交鏈表