content: import java.io.*;
  import java.math.*;
  import java.security.*;
  import java.text.*;
  import java.util.*;
  import java.util.concurrent.*;
  import java.util.regex.*;
  
  class Result {
  
      /*
       * Complete the 'stockmax' function below.
       *
       * The function is expected to return a LONG_INTEGER. The function accepts
       * INTEGER_ARRAY prices as parameter.
       */
  
      public static long stockmax(List<Integer> prices) {
          int n = prices.size();
          long maxSoFar = prices.get(n - 1), profit = 0;
          for (int i = n - 2; i >= 0; i--) {
              // if current price is greater than max,update max
              if (prices.get(i) > maxSoFar)
                  maxSoFar = prices.get(i);
              else
                  // profit will be after selling the stock at lower price
                  profit += maxSoFar - prices.get(i);
          }
          return profit;
          // Write your code here
  
      }
  
  }
  
  public class solution {
      public static void main(String[] args) throws IOException {
          BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
          BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
  
          int t = Integer.parseInt(bufferedReader.readLine().trim());
  
          for (int tItr = 0; tItr < t; tItr++) {
              int n = Integer.parseInt(bufferedReader.readLine().trim());
  
              String[] pricesTemp = bufferedReader.readLine().replaceAll("\\s+$", "").split(" ");
  
              List<Integer> prices = new ArrayList<>();
  
              for (int i = 0; i < n; i++) {
                  int pricesItem = Integer.parseInt(pricesTemp[i]);
                  prices.add(pricesItem);
              }
  
              long result = Result.stockmax(prices);
  
              bufferedWriter.write(String.valueOf(result));
              bufferedWriter.newLine();
          }
  
          bufferedReader.close();
          bufferedWriter.close();
      }
  }
  