短但让人眼前一黑的代码

#include<iostream>
using namespace std;
int a[1000000],cnt;
int t(int c){
	int answer=1;
	while(c--)answer*=10;
	return answer;
}
int main(){
	freopen("lock.in","r",stdin);
	freopen("lock.out","w",stdout);
	int n;
	cin>>n;
	for(int i=1;i<=n;i++){
		int S=0;
		for(int j=1;j<=5;j++){
			int s;
			cin>>s;
			S=S*10+s;
		}
		for(int j=0;j<5;j++)
			for(int k=1;k<=9;k++){
				a[(S+k*t(j))%t(j+1)+S/t(j+1)*t(j+1)]++;
				if(j!=4)a[(S/t(j)+k)%10*t(j)+(S/t(j+1)+k)%10*t(j+1)+S/t(j+2)*t(j+2)+S%t(j)]++;
			}
	}
	for(int i=0;i<1000000;i++)if(a[i]==n)cnt++;
	cout<<cnt;
	fclose(stdin);
	fclose(stdout);
	return 0;
}