1491. Average Salary Excluding the Minimum and Maximum Salary
给你一个阵列 salary 其中的元素不重复，salary [i] 表示第 i 个员工的薪水，求出除
了最多和最少薪水的员工的平均薪水。
Example:
Input: salary = [4000,3000,1000,2000]
Output: 2500.00000
Explanation: Minimum salary and maximum salary are 1000 and 4000 respectively.
Average salary excluding minimum and maximum salary is (2000+3000) / 2 = 2500
Input: salary = [1000,2000,3000]
Output: 2000.00000
Explanation: Minimum salary and maximum salary are 1000 and 3000 respectively.
Average salary excluding minimum and maximum salary is (2000) / 1 = 2000
思路：
1.遍历全部薪水并记录薪水最多和最少是多少，并把全部薪水加总。
2.把加总后的薪水减去最多和最少除以 n-2 就是平均。
Java Code：