POJ 3292Semi-prime H-numbers（筛法变形）

来源：互联网发布：linux trace 命令编辑：程序博客网时间：2024/05/11 14:40

我只能说这个水筛法写了我两个小时。。没有爱了。

#pragma warning(disable:4996)#include <cstdio>#include <cstring>#include <algorithm>#include <iostream>using namespace std;const long long N = 1000001;long long H[300000];int tol;bool prime[300000];bool semi[300000];int ans[300000];int main() {tol = 0;for (int i = 0; 4 * i + 1 <= N; i++) {H[tol++] = 4 * i + 1;}memset(prime, true, sizeof prime);prime[0] = false;for (int i = 1; i < tol; i++) {if (prime[i]) {int s = 1;long long j;for (j = H[s] * H[i]; s < tol&&j <= N; j = H[i] * H[s]) {prime[(j - 1) / 4] = false;s++;}}}memset(semi, false, sizeof semi);for (int i = 1; i < tol; i++) {if (prime[i]) {for (int j = 1; j < tol; j++) {if (prime[j]) {long long tmp = (long long)H[i] * H[j];if (tmp <= N) {semi[(tmp - 1) / 4] = true;}else break;}}}}memset(ans, 0, sizeof ans);for (int i = 1; i < tol; i++) {ans[i] = ans[i - 1];if (semi[i])ans[i]++;}int h;while (scanf("%d", &h)) {if (!h)break;int id = (h - 1) / 4;printf("%d %d\n", h, ans[id]);}return 0;}

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