Omkar and Waterslide

### 题目大意 Omkar 想在它的公园里做一个水滑道，这个滑道分为 $n$ 段，水将会从第 $n$ 段流向第 $1$ 段，因此我们需要让滑道的高度形成一个不下降的序列（从 $1$ 到 $n$ 不下降）。 现在给出每一段的高度，在一次操作中，你可以选择一段不下降的区间 $[l,r]$，然后将区间内的滑道高度 $+1$。 问最少需要多少次操作可以使得滑道的高度形成一个不下降的序列。

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 $ .

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 $ .

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.

3
4
5 3 2 5
5
1 2 3 5 3
3
1 1 1

3
2
0

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, \textbf{4}, \textbf{4}, 5] \to [5, \textbf{5}, \textbf{5}, 5] $ In the third test case, the array is already nondecreasing, so Omkar does $ 0 $ operations.