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//https://www.geeksforgeeks.org/trapping-rain-water/
#include <iostream>
using namespace std;

int areafunc (int a[], int n) {
    // left[i] contains height of tallest bar to the
    // left of i'th bar including itself
    int left[n];

    // Right [i] contains height of tallest bar to
    // the right of ith bar including itself
    int right[n];

    // Initialize result
    int water = 0;

    // Fill left array
    left[0] = arr[0];
    for (int i = 1; i < n; i++)
       left[i] = max(left[i-1], arr[i]);

    // Fill right array
    right[n-1] = arr[n-1];
    for (int i = n-2; i >= 0; i--)
       right[i] = max(right[i+1], arr[i]);

    // Calculate the accumulated water element by element
    // consider the amount of water on i'th bar, the
    // amount of water accumulated on this particular
    // bar will be equal to min(left[i], right[i]) - arr[i] .
    for (int i = 0; i < n; i++)
       water += min(left[i],right[i]) - arr[i];

    return water;
}

int main() {
    int t;
    cin>>t;
    while (t-->0) {
        int n;
        cin>>n;
        int a[n];
        for (int i=0;i<n;i++)
            cin>> a[i];
        cout<< "\n"<<areafunc (a, n)  ;
    }
}