素数最短距离算法

#include <cstdio>#include <cstring>#include <cmath>using namespace std;#define MAX_LENGTH 50000001bool prime[MAX_LENGTH];void CreatePrimeTable(){int i, j;memset(prime, true, sizeof(prime)); // 初始化全为1prime[0] = prime[1] = false;  // 0和1不是素数for (i = 2; i * i < MAX_LENGTH; i++){if (prime[i]) // 如果是素数{// 如果i是素数，那么能整除i的肯定不是素数for (j = i * 2; j < MAX_LENGTH; j += i){prime[j] = false;}}}}int main(){ int number = 0;long prevDist = 0, // 当前素数与前一个素数的距离 nextDist = 0; // 当前素数与后一个素数的距离int i = 0, j = 0;CreatePrimeTable();while (scanf("%d", &number) != EOF){prevDist = 0;nextDist = 0;if (prime[number]) // 如果是素数{printf("%d ", number);for (i = number - 1; i >= 2; i--){if (prime[i] != 0){prevDist = number - i;break;}}for (i = number + 1; i < MAX_LENGTH; i++){if (prime[i] != 0){nextDist = i - number;break;}}printf("%d\n", prevDist < nextDist ? prevDist : nextDist);}else{printf("%d不是素数\n", number);}}return 0;}