/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner sc = new Scanner(System.in);
		int t = sc.nextInt();
		for(int i=0;i<t;i++){
			int n = sc.nextInt();
			int [] arr= new int[n];
			for(int j=0;j<n;j++){
				arr[j]=sc.nextInt();
			}
			int minDiff = Integer.MAX_VALUE;
			for(int j=0;j<n-1;j++){
				minDiff=Math.min(arr[j+1]-arr[j],minDiff);
			}
			if(minDiff<0){
				System.out.println(0);
			}
			else{
				System.out.println((minDiff/2)+1);
			}
		}
	}
}

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NAoyCjEgMQo0CjEgOCAxMCAxMwozCjEgMyAyCjMKMSA5IDE0

4
2
1 1
4
1 8 10 13
3
1 3 2
3
1 9 14