Leetcode刷题记录_20181023

Posted 2021-01-14 autoyzz

160.Intersection of Two Linked Lists

查找并返回AB链表中的交点，若无返回None

方法1：

计算A、B两个链表长度，优先循环长度长的链表，长度差次循环后，依次对比AB

 1 class Solution(object):
 2     def getIntersectionNode(self, headA, headB):
 3         """
 4         :type head1, head1: ListNode
 5         :rtype: ListNode
 6         """
 7         
 8         a = headA
 9         b = headB
10         anum = 0
11         bnum = 0
12         if not a and not b: return None
13         while a:
14             anum +=1
15             a = a.next
16         while b:
17             bnum +=1
18             b = b.next
19         flag = abs(anum-bnum)
20         if anum>bnum:
21             a = headA
22             b = headB
23             for i in range(flag):
24                 a = a.next
25             while a and b:
26                 if a.val == b.val:
27                     return a
28                 a = a.next
29                 b = b.next
30             return None
31         else:
32             a = headA
33             b = headB
34             for i in range(flag):
35                 b = b.next
36             while a and b :
37                 if a.val == b.val:
38                     return b
39                 a = a.next
40                 b = b.next
41             return None
42         

View Code

方法2：

将AB组合，A循环到链表末尾转至B，B循环到链表末尾转至A，如有相同Node，返回

 1 class Solution(object):
 2     def getIntersectionNode(self, headA, headB):
 3         """
 4         :type head1, head1: ListNode
 5         :rtype: ListNode
 6         """
 7        
 8         if not headA or not headB: return None
 9         a = headA
10         b = headB
11         flag = 0
12         while flag <=2:
13             if a.val == b.val:
14                 return a
15             a = a.next
16             b = b.next
17             if a == None:
18                 a = headB
19                 flag +=1
20             if b == None:
21                 b = headA
22                 flag +=1
23         return None

View Code

167.Two Sum II - Input array is sorted

给定升序排列数组，寻找和为target的两个数字下标+1(注意：数组中必然存在唯一解)

方法：

设定头指针和尾指针，若和等于target，返回指针+1；若大于target，尾指针前移；否则头指正后移

 1 class Solution(object):
 2     def twoSum(self, numbers, target):
 3         """
 4         :type numbers: List[int]
 5         :type target: int
 6         :rtype: List[int]
 7         """
 8         a, b = 0,len(numbers)-1
 9         while a < b:
10             sum1 = numbers[a] + numbers[b]
11             if  sum1 == target:
12                 return [a+1,b+1]
13             elif sum1 > target:
14                 b -=1
15             else:
16                 a +=1
17         

View Code

168.Excel Sheet Column Title

给定数字n，返回Excel中第n列列号

A-Z对应1-26，递归方法

class Solution(object):
    def convertToTitle(self, n):
        """
        :type n: int
        :rtype: str
        """
        base = ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ‘
        if n == 0:
            return ‘‘
        return self.convertToTitle((n-1)/26) + base[(n-1)%26]

View Code