Codeforces Round #582 (Div. 3)

题意：

给出n和q，输出从q，2q，3q....n的个位数的和

题解：

很明显就是有规律，手动找循环即可

代码：

#include <bits/stdc++.h>
using namespace std;
#define ll long long
int flag[11];
ll a[10010];
int main()
{
  int t,n;
  scanf("%d",&t);
  while(t--)
  {
      ll i,n,m,cnt = 0;
      memset(flag,0,sizeof(flag));
      scanf("%lld%lld",&n,&m);
      if(n < m){
          cout<<"0"<<endl;
          continue;
      }
      int c = 0;
      for(i=m;i<=n;i+=m)
      {
          int k = i%10;
          if(flag[k]){
              break;
          }
          else{
              cnt += k;
              a[++c] = cnt;
              flag[k] = 1;
          }
      }
      if(i == n+m)
      {
          cout<<cnt<<endl;
          continue;
      }
      i -= m;
      ll ans = cnt*(n/i);
      if(n%i == 0){
          cout<<ans<<endl;
          continue;
      }
      ll k = n%i;
      ans += a[k/m];
      cout<<ans<<endl;

  }
  return 0;
}

#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int maxx = 2e5+10;
int a[maxx],ans[maxx],cnt[maxx];
int n,k,minn = 1e9+7;
void solve(int x,int y)
{
  cnt[x]++;
  ans[x] += y;
  if(cnt[x] == k)
      minn = min(minn , ans[x]);
  if(x == 0)
      return ;
  solve(x/2,y+1);
}
int main()
{
  scanf("%d%d",&n,&k);
  for(int i=1;i<=n;i++){
      scanf("%d",&a[i]);
  }
  sort(a+1,a+1+n);
  for(int i=1;i<=n;i++){
      solve(a[i],0);
  }
  cout<<minn<<endl;
  return 0;
}