【leetcode】1228.Missing Number In Arithmetic Progression

题目如下：

解题思路：题目很简单。先对数组排序，根据最大值和最小值即可求出公差，然后遍历数组，计算相邻元素的差，如果差不等于公差，即表示数字缺失。

代码如下：

class Solution(object):
    def missingNumber(self, arr):
        """
        :type arr: List[int]
        :rtype: int
        """
        arr.sort()
        diff = (arr[-1] - arr[0])/(len(arr))
        for i in range(len(arr)-1):
            if arr[i] + diff != arr[i+1]:
                return arr[i] + diff
        return arr[0]