667d.cpp

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*/                              
#include<bits/stdc++.h>
using namespace std;
 
#define fastio ios_base::sync_with_stdio(0); cin.tie(0)
#define LL long long 
#define mod 1000000007 
#define all(v) v.begin(),v.end()
#define pr(v) pair<v,v>
#define pb push_back
#define FOR(i, j, k) for (auto i=j ; i<k ; i++)
#define ROF(i, j, k) for (auto i=j ; i>=k ; i--) 
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false); debug("%s time : %.4fs", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))

const long long INF = 1e18;
const long long MAX = 2e5+10;
int sum(LL x){
  int d=0;
  while(x) d+=x%10,x/=10;
  return d;
}

int dig(LL x){
  int d = -1;
  while(x) {
    if(x%10>0) {d=x%10; break;}
    x/=10;
  } 
  return d;
}

int main(){
    fastio;
    int t=1;  cin>>t;
    while(t--){
        LL n,s; cin>>n>>s;
        if(sum(n)<=s) { cout<<0<<"\n"; continue;  }
        LL N=n; int i=0;
        while(sum(N)>s && i<20){
            LL p= pow(10,i);
            LL temp = N;
            if(i>0) { LL k = pow(10,i); temp=(temp/k)*k;  } 
            int d = dig(temp); 
            d= (10-d)%10;
            temp +=(p*d);
            if(sum(temp)>s) N=temp;
            else {       
              //cout<<d<<" "<<temp<<", ";
              FOR(j,0,d+1) {
                  LL x = temp + p*j;// cout<<x<<" ";
                  if(sum(x)<=s) {N=x; break;}
              }
              break;
            }// cout<<N<<" ;";
            i++; 
        }
        cout<<(N-n)<<"\n";
    }   
}