1029D - Concatenated Multiples - CodeForces Solution

#include<cstdio>
#include<map>
using namespace std;
int N,K;
int A[2<<17],L[2<<17];
main()
{
scanf("%d%d",&N,&K);
for(int i=0;i<N;i++)
{
scanf("%d",&A[i]);
int t=A[i];
while(t)t/=10,L[i]++;
}
long long ans=0;
map<int,int>mp[11];
for(int i=0;i<N;i++)
{
int t=A[i]%K;
for(int j=1;j<=10;j++)
{
t=(long long)t*10%K;
mp[j][t]++;
if(j==L[i])
{
if((t+A[i])%K==0)ans--;
}
}
}
for(int i=0;i<N;i++)
{
int t=(K-A[i]%K)%K;
ans+=mp[L[i]][t];
}
printf("%lld\n",ans);
}