Zap

https://blog.csdn.net/qq_42555009/article/details/87253503

#include <bits/stdc++.h>

using namespace std;
const int N=50005;
int mu[N],pr[N],tot,vis[N],sum[N];
typedef long long ll;
void init() {
    mu[1] = 1;
    for (int i = 2; i < N; i++) {
        if (!vis[i]) {
            pr[++tot] = i;
            mu[i] = -1;
        }
        for (int j = 1; j <= tot && i * pr[j] < N; j++) {
            vis[i * pr[j]] = 1;
            if (i % pr[j] == 0) break;
            mu[i * pr[j]] = -mu[i];
        }
    }
    for (int i = 1; i < N; i++) sum[i] = sum[i - 1] + mu[i];
}

int main() {
    int _, b, d, k;
    scanf("%d", &_);
    init();
    while (_--) {
        scanf("%d%d%d", &b, &d, &k);
        if (k == 0) {
            printf("0
");
            continue;
        }
        ll ans = 0;
        b /= k;
        d /= k;
        for (int i = 1, nxt; i <= min(b, d); i = nxt + 1) {
            nxt = min(b / (b / i), d / (d / i));
            ans += 1ll * (sum[nxt] - sum[i - 1]) * (b / i) * (d / i);
        }
        printf("%lld
", ans);
    }
    return 0;
}