ZOJ GCD Expectation

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <string>
#include <map>
#include <cmath>
#include <math.h>
#include <cstdio>
#define LL long long
using namespace std;
const int MAXN = 1000000 + 10;
const int MOD = 998244353;
LL pow_mod(LL a, LL b)
{
    LL res = 1;
    while(b)
    {
        if(b & 1) res = res * a % MOD;
        a = a * a % MOD;
        b >>= 1;
    }
    return res;
}
int A[MAXN], B[MAXN];
int dp[MAXN];
int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        int n, k;
        memset(B, 0, sizeof(B));
        int Max = 0;
        scanf("%d%d", &n, &k);
        for(int i=1;i<=n;i++)
        {
            scanf("%d", &A[i]);
            B[A[i]]++;
            Max = max(Max, A[i]);
        }
        memset(dp, 0, sizeof(dp));
        LL ans = 0;
        for(int i=Max;i>=1;i--)
        {
            int c = 0;
            for(int j=i;j<=Max;j+=i)
            {
                c += B[j];
                if(j > i) dp[i] = (dp[i] - dp[j] + MOD) % MOD;
            }
            dp[i] = (dp[i] + pow_mod(2, c) - 1 + MOD) % MOD;
            ans = (ans + pow_mod(i, k) * dp[i]) % MOD;
        }
        printf("%lld\n", ans);
    }
    return 0;
}

ZOJ GCD Expectation

原文：http://blog.csdn.net/moguxiaozhe/article/details/45101009