Chocolate Distribution ProblemChocolate 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}.
Your Task:
You don't need to take any input or print anything. Your task is to complete the function findMinDiff() which takes array A[ ], N and M as input parameters and returns the minimum possible difference between maximum number of chocolates given to a student and minimum number of chocolates given to a student.

Expected Time Complexity: O(N*Log(N))
Expected Auxiliary Space: O(1)

Constraints:
1 ≤ T ≤ 100
1 ≤ N ≤ 105
1 ≤ Ai ≤ 109
1 ≤ M ≤ N
solutions:


// Here we use substring concept and we take i at start and j at i+m-1 and increment it as 

class Solution
{
    public long findMinDiff (ArrayList<Integer> a, int n, int m)
    {
        long ans = Integer.MAX_VALUE;
         Collections.sort(a);
        int i=0,j = i+(m-1);
        while(j<n){
            ans = Math.min(ans, a.get(j++).intValue() - a.get(i++).intValue());     //here we use .get.intValue() because it a ArrayList
        }
        return ans;
        
    }
}