Minimise the heights

'''
Given an array arr[] denoting heights of N towers and a positive integer K.

For each tower, you must perform exactly one of the following operations exactly once.

Increase the height of the tower by K.
Decrease the height of the tower by K ( you can do this operation only if the height of the tower is greater than or equal to K)
Find out the minimum possible difference between the height of the shortest and tallest towers after you have modified each tower.
'''

class Solution:
    def getMinDiff(self, arr, n, k):
        arr.sort()
        res = arr[-1]-arr[0]
        n=len(arr)
        #We have to decrease the right end  must
        #we have to increase the left end must.Both are must. Because we want to reduce difference
        #Now we choose any two consecutive elements
        #X,Y we will increase X and decrease Y so that we minimise the our target.
        #To compare target we need to findout temp min and temp max after modifying the array values.
        #After modifying we will compare the tmax tmin diff and take mimimum of both.
        for i in range(1,n):
            X=arr[i]
            Y=arr[i-1]
            if arr[i]<k: #since in question he gave height cant be negative we shall skip it
            tmin = min(arr[0]+k , X-k )#you need not do min op arr[i-1]+k because we know arr[i-1]<arr[i]
            tmax = max(arr[-1]-k , Y+k)#you need not do max oparr[i]-k because we know arr[i]<arr[-1]
            res=min(res,tmax-tmin)
        return res