//μ's forever
#include <bits/stdc++.h>
#define N 300005
#define ll long long
//#define getchar nc
using namespace std;
inline char nc(){
    static char buf[100000],*p1=buf,*p2=buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;
}
inline int read()
{
    register int x=0,f=1;register char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9')x=(x<<3)+(x<<1)+ch-'0',ch=getchar();
    return x*f;
}
inline void write(register int x)
{
    if(!x)putchar('0');if(x<0)x=-x,putchar('-');
    static int sta[20];register int tot=0;
    while(x)sta[tot++]=x%10,x/=10;
    while(tot)putchar(sta[--tot]+48);
}
int T,n,a[N];
ll ans=0;
int main()
{
    T=read();
    while(T--){
        n=read();
        for(int i=1;i<=n;++i) a[i]=read();
        ans=0;
        int mn=a[n];
        for(int i=n-1;i>=1;--i){
            ans+=mn-a[i];
            mn=min(mn,a[i]);
        }
        printf("%lld\n",ans);
    }
    return 0;
}