Agresive cow problem

#1

getting wrong answer.
and pls explain to me the isvalid method by commenting out step by step that what is happening

#2

import java.util.*; public class Main { public static void main(String args[]) { Scanner sc = new Scanner(System.in); long N = sc.nextLong(); int temp = (int)N; long c = sc.nextInt(); long a[] = new long[temp]; for(int i =0;i<N;i++) { a[i]=sc.nextLong(); } Arrays.sort(a); System.out.println(cowDist(N,c,a)); } public static long cowDist(long n, long c, long[] a) { long s=0; long e=a[a.length-1]; long ans =0; while(s<=e) { long mid=(s+e)/2; if(isValid(a,n,c,ans)) { ans = mid; s=mid+1; }else { e=mid-1; } } return ans; } public static boolean isValid(long[] a, long n ,long c, long ans) { long pos=a[0]; long cow=1; for(int i =1;i<n;i++) { if(a[i]-pos>=ans) { pos=a[i]; cow++; if(cow==c) { return true; } } } if(cow<c) { return false; } return true; } }

#3 
import java.util.*;
public class Main {
    public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		
		int c = sc.nextInt();
		int a[] = new int[N];
		for(int i =0;i<N;i++)
		{
			a[i]=sc.nextInt();
		}
		Arrays.sort(a);
		System.out.println(cowDist(N,c,a));

	}
	
	public static int cowDist(int n, int c, int[] a) {
		int s=0; int e=a[n-1];
		int ans =0;
		while(s<=e) {
			int mid=(s+e)/2;
			if(isValid(a,n,c,mid)) {//you were passing ans as the fourth argument in isValid function 
				ans = mid;
				s=mid+1;
				
			}else {
				e=mid-1;
			}
			
		}
		return ans;
		
	}
	
	public static boolean isValid(int[] a, int n ,int c, int ans)  {
		int pos=a[0];
		int cow=1;
		for(int i =1;i<n;i++) {
			if(a[i]-pos>=ans) {
				pos=a[i];
				cow++;
				if(cow==c) {
					return true;
				}
			}
		}
		return false;//if we reach here then it means that we are not able to place c no of cows
    }
}
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