整数拼接

哈希表+枚举

#include<cstring>
#include<iostream>
#define N 100010

typedef long long LL;
int n,k;
int a[N],s[11][N];

int main()
{
    scanf("%d%d",&n,&k);

    for(int i = 0;i < n;i ++)   scanf("%d",&a[i]);
    //Aj*10^i(mod k) 预处理恒等式=>左边
    for(int j = 0;j < n;j ++)
    {
        LL t = a[j] % k;
        for(int i = 0;i < 11;i ++)
        {
            s[i][t] ++;     //把等式左边所有存在的情况标记
            t = t * 10 % k;
        }
    }

    LL res = 0;
    //-Ai (mod k) 预处理恒等式=>右边
    for(int i = 0;i < n;i ++)
    {
        LL t = a[i] % k;
        int len = to_string(a[i]).size();
        res += s[len][(k - t) % k];

        //判断Aj != Ai
        LL r = t;
        while(len --)   r = r * 10 % k;
        if(r == (k - t) % k)    res --;
    }

}