136. Single Number； 137. Single Number II；260. Single Number III; 287. Find the Duplicate Number

#136. Single Number
class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        single=[]
        for i in range(len(nums)):
            if nums[i] not in single:
                single.append(nums[i] )
            else:
                single.remove(nums[i])
        return single[0]

class Solution(object):

    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        hash_table={}
        for i in nums:
            if i not in hash_table:
                hash_table[i]=1
            else:
                hash_table[i] += 1
                if hash_table[i] >=3:
                    del hash_table[i]
        return hash_table.keys()[0]

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        return (2*sum(set(nums)) - sum(nums))

#137. Single Number II
class Solution(object):

    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        hash_table={}
        for i in nums:
            if i not in hash_table:
                hash_table[i]=1
            else:
                hash_table[i] += 1
                if hash_table[i] >=3:
                    del hash_table[i]
        return hash_table.keys()[0]

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        return (3*sum(set(nums)) - sum(nums))/2

260. Single Number III
class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        diff = 2*sum(set(nums)) - sum(nums)
        for i in nums:
            j=diff - i
            if j in nums:
                return [j,i]

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        hash_table={}
        for i in nums:
            if i not in hash_table:
                hash_table[i]=1
            else:
                hash_table[i] += 1
                if hash_table[i] ==2:
                    del hash_table[i]
        return hash_table.keys()

287. Find the Duplicate Number
class Solution:
    def findDuplicate(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        hash_table ={}
        for i in nums:
            if i not in hash_table:
                hash_table[i]=1
            else:
                hash_table[i]+=1
                if hash_table[i] >1:
                    return i