题解

#include <iostream>
using namespace std;
const int N = 100010;
const int mod = 1e4+7;
int n,m;
int idx[N],color[N];
int cnt[N][2];
int sum[N][2];
int main()
{
    cin>>n>>m;
    for(int i = 1;i <= n;i++)
    {
        cin>>idx[i];
        idx[i] = idx[i]%mod;
    }
    for(int i = 1;i <= n;i++)
    {
        int c;
        cin>>c;
        color[i] = c;
        cnt[c][i%2]++;
        sum[c][i%2] = (sum[c][i%2]+idx[i])%mod;
    }
    long long ans = 0;
    for(int i = 1;i <= n;i++)
    {
        int c = color[i];
        ans += i*((sum[c][i%2]+((cnt[c][i%2]-2)*idx[i]%mod+mod))%mod)%mod;
        ans %= mod;
    }
    cout<<ans;
    return 0;
}