[noip2015 pjt3]求和

思维题

把给定式子拆掉（分配律），前缀和维护

注意long long！！！

注意%%%%%%！！！

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define maxn 100233
#define maxm 100233
#define ll long long
const ll MOD=10007;
ll n,m;
ll ans=0;
ll num[maxn],col[maxn];
ll cnt[maxm][2],number[maxm][2],rSum[maxm][2],sum[maxm][2];
//cnt:同颜色同奇偶的个数；
//number:序号的前缀和；sum:数字的前缀和；rSum:序号*数字的前缀和；
int main(){
    scanf("%lld%lld",&n,&m);
    for (ll i=1;i<=n;i++) scanf("%lld",&num[i]);
    for (ll i=1;i<=n;i++) scanf("%lld",&col[i]);
    for (ll i=1;i<=n;i++){
        ll c=col[i],x=i%2;
        cnt[c][x]++;
        if (cnt[c][x]>1) {
            ans+=(number[c][x]*num[i]%MOD+rSum[c][x]+(cnt[c][x]-1)*i*num[i]%MOD
            +i*sum[c][x]%MOD)%MOD;
        }
        ans%=MOD;
        number[c][x]=(number[c][x]+i)%MOD;
        rSum[c][x]=(rSum[c][x]+i*num[i])%MOD;
        sum[c][x]=(sum[c][x]+num[i])%MOD;
    }
    printf("%lld
",ans);
    return 0;
}