Leetcode刷题记录-20181022

Posted 2021-01-14 autoyzz

136. Single Number

方法一：建立字典，依次循环；

 1 class Solution:
 2     def singleNumber(self, nums):
 3         """
 4         :type nums: List[int]
 5         :rtype: int
 6         """
 7         dict1 = {}
 8         for i in nums:
 9             if i not in dict1:
10                 dict1[i]= 1
11             else:
12                 dict1[i] +=1
13         for i in dict1:
14             if dict1[i] ==1:
15                 return i

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方法二：使用集合set(),返回集合差

1 class Solution:
2     def singleNumber(self, nums):
3         """
4         :type nums: List[int]
5         :rtype: int
6         """
7         
8         return 2*sum(set(nums))-sum(nums)

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141. Linked List Cycle  

判断是否链表中是否有环

思想：设定快慢指针，如快指针为Null 或者快指针.next 为null，那么没有环；

 1 class Solution(object):
 2     def hasCycle(self, head):
 3         """
 4         :type head: ListNode
 5         :rtype: bool
 6         """
 7         
 8         if not head:
 9             return False
10         fast = head.next
11         slow = head
12         while (slow != fast):
13             if fast == None or fast.next == None:
14                 return False
15             fast = fast.next.next
16             slow = slow.next
17            
18         return True

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155. Min Stack

 1 class MinStack:
 2 
 3     def __init__(self):
 4         """
 5         initialize your data structure here.
 6         """
 7         self.stack = []
 8         self.min = float(‘inf‘)
 9         
10 
11     def push(self, x):
12         """
13         :type x: int
14         :rtype: void
15         """
16         self.stack.append(x)
17         self.min = min(self.min, x)
18 
19     def pop(self):
20         """
21         :rtype: void
22         """
23         if self.stack.pop() == self.min :
24             self.min = min(self.stack) if self.stack else float(‘inf‘)
25         
26         
27 
28     def top(self):
29         """
30         :rtype: int
31         """
32         return self.stack[-1]
33 
34     def getMin(self):
35         """
36         :rtype: int
37         """
38         return self.min

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