codeforces 1409D（题意描述）

#include<bits/stdc++.h>
#define x first
#define y second
#define PB push_back
#define mst(x,a) memset(x,a,sizeof(x))
#define all(a) begin(a),end(a)
#define rep(x,l,u) for(ll x=l;x<u;x++)
#define rrep(x,l,u) for(ll x=l;x>=u;x--)
#define sz(x) x.size()
#define IOS ios::sync_with_stdio(false);cin.tie(0);
using namespace std;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef pair<char,char> PCC;
typedef long long ll;
typedef pair<ll,ll> PLL;
const int N=2*1e5+10;
const int M=1e5+10;
const int INF=0x3f3f3f3f;
const int MOD=1e9+7;
ll digitsum(ll n){
    ll res=0;
    while(n){
        res+=n%10;
        n/=10;
    }
    return res;
}
ll dg(ll n,ll s){
    if(digitsum(n)<=s) return 0;
    if(n%10==0) return dg(n/10,s)*10;
    return dg(n+10-n%10,s)+10-n%10;
}
void solve(){
    ll n,s;cin>>n>>s;
    cout<<dg(n,s)<<endl;
}
int main(){
    IOS;
    //freopen("test.txt", "r", stdin);
    //freopen("test.txt", "w", stdout);
    int t;cin>>t;
    while(t--)
        solve();
    return 0;
}