MissingNumber.py

### Python Solution 1:
class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        res = 0
        n = len(nums)
        nums_set = set(nums)
        for num in range(n+1):
            if num not in nums_set:
                return num
        return res
### Python Solution 2:
# -*- coding:utf-8 -*-
class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        res = 0;
        n = len(nums)
        x = range(n+1)
        x = list(x)           ### Python3 需要用list转换成数组
        res = sum(x)-sum(nums)
        return res
      
      
 # -*- coding:utf-8 -*-
class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        n = len(nums)
        res = n
        for i in range(n):
            res = res ^ nums[i]
            res = res ^ i
        return res
### Python Solution 3:
# -*- coding:utf-8 -*-
class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        nums = sorted(nums)
        n = len(nums)
        if nums[-1] != n:
            return n
        for i in range(0,n):
            if i!=nums[i]:
                return i