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}.


Source code:
class Solution{
    public:
    long long findMinDiff(vector<long long> a, long long n, long long m){
    //code
    sort(a.begin(),a.end());
    int min=INT_MAX;
    for(int i=0;i+m-1<n;i++){
        int d=a[i+m-1]-a[i];
        
        if(d<min){
            min=d;
        }
    }
    return min;
    }   
};