// Given an array arr[] of N non-negative integers representing the height of blocks. 
// If width of each block is 1, compute how much water can be trapped between the blocks during the rainy season. 

//Time Complexity: O(N)
//Auxiliary Space: O(1)

import java.io.*;
import java.util.*;
import java.lang.*;


class Main {

	public static void main (String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int t = Integer.parseInt(br.readLine().trim()); //Inputting the testcases
		while(t-->0){
		  
		    //size of array
		    int n = Integer.parseInt(br.readLine().trim());
		    int arr[] = new int[n];
		    String inputLine[] = br.readLine().trim().split(" ");
		    
		    //adding elements to the array
		    for(int i=0; i<n; i++){
		        arr[i] = Integer.parseInt(inputLine[i]);
		    }
		    
		    Solution obj = new Solution();
		    
		    //calling trappingWater() function
		    System.out.println(obj.trappingWater(arr, n));
		}
	}
}

class Solution{
    
    // arr: input array
    // n: size of array
    // Function to find the trapped water between the blocks.
    static int trappingWater(int arr[], int n) { 
    // initialize output
    int result = 0;

    // maximum element on left and right
    int left_max = 0, right_max = 0;

    // indices to traverse the array
    int lo = 0, hi = n - 1;

    while (lo <= hi) {
        if (arr[lo] < arr[hi]) {
            if (arr[lo] > left_max)
                // update max in left
                left_max = arr[lo];
            else
                // water on curr element = max - curr
                result += left_max - arr[lo];
            lo++;
        }
        else {
            if (arr[hi] > right_max)
                // update right maximum
                right_max = arr[hi];
            else
                result += right_max - arr[hi];
            hi--;
        }
    }

    return result;
    } 
}

/* Test Case:
Input:
N = 6
arr[] = {3,0,0,2,0,4}
Output:
10
Explanation: 
 ____|
|    |
|  | |
|  | |
300204

Total Water Trapped: 3+3+1+3 = 10
 */