Chocolate Distribution Problem

Given an array A[ ] of positive integers of size N, where each value represents the number of chocolates in a packet. Each packet can have a variable number of chocolates. There are M students, the task is to distribute chocolate packets among M students such that :
1. Each student gets exactly one packet.
2. The difference between maximum number of chocolates given to a student and minimum number of chocolates given to a student is minimum.

Example 1:

Input:
N = 8, M = 5
A = {3, 4, 1, 9, 56, 7, 9, 12}
Output: 6
Explanation: The minimum difference between 
maximum chocolates and minimum chocolates 
is 9 - 3 = 6 by choosing following M packets :
{3, 4, 9, 7, 9}.

Example 2:

Input:
N = 7, M = 3
A = {7, 3, 2, 4, 9, 12, 56}
Output: 2
Explanation: The minimum difference between
maximum chocolates and minimum chocolates
is 4 - 2 = 2 by choosing following M packets :
{3, 2, 4}.

method 1:

1)sort the given vector or the array

2)point i to first element of sorted array and point j to m-1 steps ahead of i ie. j=i+m-1

3)now traverse through array till j<n and keep find the difference between a[j]-a[i] 
increment i and j everytime

4)find the min difference

c++ implementation:

    long long findMinDiff(vector<long long> a, long long n, long long m)
    {
        sort(a.begin(),a.end());
        long long i=0;long long j=i+m-1; long long mi=INT_MAX;
       while(j<n)
       {
           if(a[j]-a[i]<mi)
           mi=a[j]-a[i];
           
           i++;
           j++;
       }
       return mi;
    } 

Time Complexity: O(nlogn) 

space Complexity: O(1)