Ultraviolet A 11105-semi-prime H-numbers (number theory)

Link to the question: Ultraviolet A 11105-semi-prime H-Numbers

H-number is 4? K + 1 (K is not negative), H-composites is the number of factors containing H-number (not including itself), the inverse time is H-Prime, given n, h-composites.

Solution: first, use the factorial method to find the H-prime in the range, and then enumerate the two to determine whether the product is within the range.

#include <cstdio>#include <cstring>const int maxn = 1e6+5;typedef long long ll;int v[maxn], prime[maxn], cp;void primeHtable(int n) {    cp = 0;    memset(v, 0, sizeof(v));    for (int i = 5; i < n; i += 4) {        if (v[i])            continue;        prime[cp++] = i;        for (int j = i * 2; j < n; j += i)            v[j] = 1;    }}int solve (int n) {    int ans = 0;    memset(v, 0, sizeof(v));    for (int i = 0; prime[i] < n && i < cp; i++) {        if ((ll)prime[i] * prime[i] > n)            break;        for (int j = i; prime[j] < n && j < cp; j++) {            ll u = (ll)prime[i] * prime[j];            if (u > n)                break;            if (v[u])                continue;            ans++;            v[u] = 1;        }    }    return ans;}int main () {    primeHtable(maxn);    int n;    while (scanf("%d", &n) == 1 && n) {        printf("%d %d\n", n, solve(n));    }    return 0;}