Solve in Python:
Omkar is building a waterslide in his water park, and he needs your help to ensure that he does it as efficiently as possible.

Omkar currently has $n$ supports arranged in a line, the $i$-th of which has height $a_i$. Omkar wants to build his waterslide from the right to the left, so his supports must be nondecreasing in height in order to support the waterslide. In $1$ operation, Omkar can do the following: take any contiguous subsegment of supports which is nondecreasing by heights and add $1$ to each of their heights. 

Help Omkar find the minimum number of operations he needs to perform to make his supports able to support his waterslide!

An array $b$ is a subsegment of an array $c$ if $b$ can be obtained from $c$ by deletion of several (possibly zero or all) elements from the beginning and several (possibly zero or all) elements from the end.

An array $b_1, b_2, \dots, b_n$ is called nondecreasing if $b_i\le b_{i+1}$ for every $i$ from $1$ to $n-1$.


-----Input-----

Each test contains multiple test cases. The first line contains the number of test cases $t$ ($1 \leq t \leq 100$). Description of the test cases follows.

The first line of each test case contains an integer $n$ ($1 \leq n \leq 2 \cdot 10^5$) — the number of supports Omkar has.

The second line of each test case contains $n$ integers $a_{1},a_{2},...,a_{n}$ $(0 \leq a_{i} \leq 10^9)$ — the heights of the supports.

It is guaranteed that the sum of $n$ over all test cases does not exceed $2 \cdot 10^5$.


-----Output-----

For each test case, output a single integer — the minimum number of operations Omkar needs to perform to make his supports able to support his waterslide.


-----Example-----
Input
3
4
5 3 2 5
5
1 2 3 5 3
3
1 1 1

Output
3
2
0



-----Note-----

The subarray with which Omkar performs the operation is bolded.

In the first test case:

First operation:

$[5, 3, \textbf{2}, 5] \to [5, 3, \textbf{3}, 5]$

Second operation:

$[5, \textbf{3}, \textbf{3}, 5] \to [5, \textbf{4}, \textbf{4}, 5]$

Third operation:

$[5,...
for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    ans=0
    for i in range(1,n):
        if a[i]<a[i-1]:
            ans+=a[i-1]-a[i]
    print(ans)