Leetcode刷題記錄-20181022

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136. Single Number

方法一：建立字典，依次迴圈；

 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]= 111             else:12                 dict1[i] +=113         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: int6         """7         8         return 2*sum(set(nums))-sum(nums)

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141. Linked List Cycle  

判斷是否鏈表中是否有環

思想：設定快慢指標，如快指標為Null 或者快指標.next 為null，那麼沒有環；

 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 False10         fast = head.next11         slow = head12         while (slow != fast):13             if fast == None or fast.next == None:14                 return False15             fast = fast.next.next16             slow = slow.next17            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: int14         :rtype: void15         """16         self.stack.append(x)17         self.min = min(self.min, x)18 19     def pop(self):20         """21         :rtype: void22         """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: int31         """32         return self.stack[-1]33 34     def getMin(self):35         """36         :rtype: int37         """38         return self.min

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Leetcode刷題記錄-20181022