import std.algorithm;
import std.conv;
import std.range;
import std.stdio;
import std.string;

void main ()
{
	auto tests = readln.strip.to !(int);
	foreach (test; 0..tests)
	{
		auto n = readln.strip.to !(int);
		auto a = readln.splitter.map !(to !(int)).array;
		long res = 0;
		foreach (i; 1..n)
		{
			res += max (0, a[i - 1] - a[i]);
		}
		writeln (res);
	}
}
