uva 11246 - K-Multiple Free set(数论)

题目链接：uva 11246 - K-Multiple Free set

题目大意：给定n，k。求一个元素不大于n的子集，要求该子集的元素尽量多，而且不含两个数满足a∗k=b.

解题思路：容斥原理。f(i)=(−1)inki,取f函数的和就可以。

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
typedef long long ll;

ll solve (ll n, ll k) {
    ll ans = 0, sign = 1;
    while (n) {
        ans += sign * n;
        n /= k;
        sign *= -1;
    }
    return ans;
}

int main () {
    int cas;
    scanf("%d", &cas);
    while (cas--) {
        ll n, k;
        scanf("%lld%lld", &n, &k);
        printf("%lld\n", solve(n, k));
    }
    return 0;
}