算法竞赛入门经典5.4.2因子和阶乘

//“除非n太太太大了，否则都可运行”的版本#include <cstdio>#include <cstring>#include <cmath>bool isPrime(int x){int m = floor(sqrt(x + 0.5));for (int i = 2; i <= m; ++i){if (x % i == 0){return false;}}return true;}int main(){int prime[100];int count[100];int len = 0;memset(prime, 0, sizeof(prime));memset(count, 0, sizeof(count));for (int i = 2; i < 100; ++i){if (isPrime(i)){prime[len++] = i;}}for (int i = 0; i < len; ++i){printf("%d ", prime[i]);}int n;while (scanf("%d", &n) == 1){int i = 0;int cur = n;while (cur > 1){int tmp = cur;while (tmp > 1){if (tmp % prime[i] == 0){++count[i];tmp /= prime[i];}else{++i;}}i = 0;--cur;}int l = len - 1;while (count[l] == 0){--l;}printf("%d!=", n);for (int i = 0; i <= l; ++i){printf("%d ", count[i]);}printf("\n");memset(count, 0, sizeof(count));}return 0;}//n的阶乘不太大时才可运行的版本#include <cstdio>#include <cstring>#include <cmath>bool isPrime(int x){int m = floor(sqrt(x + 0.5));for (int i = 2; i <= m; ++i){if (x % i == 0){return false;}}return true;}int factorial(int x){int tmp = 1;for (int i = 2; i <= x; ++i){tmp *= i;}printf("%d!=%d\n", x, tmp);return tmp;}int main(){int prime[100];int count[100];int len = 0;memset(prime, 0, sizeof(prime));memset(count, 0, sizeof(count));for (int i = 2; i < 100; ++i){if (isPrime(i)){prime[len++] = i;}}for (int i = 0; i < len; ++i){printf("%d ", prime[i]);}int n;while (scanf("%d", &n) == 1){int i = 0;int tmp = factorial(n);while (tmp > 1){if (tmp % prime[i] == 0){++count[i];tmp /= prime[i];}else{++i;}}int l = len - 1;while (count[l] == 0){--l;}printf("%d!=", n);for (int i = 0; i <= l; ++i){printf("%d ", count[i]);}printf("\n");memset(count, 0, sizeof(count));}return 0;}