算法学习->素数与合数小结

一、素数打表

/*
 *  素数筛选，查找出小于等于MAXN的素数并连续存到prime[1...n]中
 *  prime[0]存素数的个数,初始为0 
 */

#include<stdio.h>
#include<string.h>

const int MAXN = ;
int prime[MAXN + ];
int vis[MAXN+];
int cnt=;

void getPrime() {
    memset(prime, , sizeof(prime));
    for (int i = ; i <= MAXN; i++) {
        if (!prime[i]) {
            prime[++prime[]] = i;
        }
        for (int j = ; j <= prime[] && prime[j] <= MAXN / i; j++) {
            prime[prime[j] * i] = ;
            if (i % prime[j] == ) {
                break;
            }
        }
    }
}
//这两个素数打表函数任选一个即可
void getPrime() {   //借助vis数组标记
    memset(prime,,sizeof(prime));
    memset(vis,,sizeof(vis));
    for(long long i=; i<=MAXN; i++) {
        if(!vis[i]) {
            prime[++cnt]=i;
        }
        for(long long j=i*i; j<=MAXN; j+=i) {
            vis[j]=;
        }
    }
}
int main() {
    //相关操作......

    return ;
}
           

二、合数分解

#include<stdio.h>
#include<string.h>

const int MAXN = ;
int prime[MAXN + ];
long long factor[][];
int fatCnt;

//  获取素数
void getPrime() {
    memset(prime, , sizeof(prime));
    for (int i = ; i <= MAXN; i++) {
        if (!prime[i]) {
            prime[++prime[]] = i;
        }
        for (int j = ; j <= prime[] && prime[j] <= MAXN / i; j++) {
            prime[prime[j] * i] = ;
            if (i % prime[j] == ) {
                break;
            }
        }
    }
    return ;
}

//  合数分解
int getFactors(long long x) {
    fatCnt = ;
    long long tmp = x;
    for (int i = ; prime[i] <= tmp / prime[i]; i++) {
        factor[fatCnt][] = ;
        if (tmp % prime[i] == ) {
            factor[fatCnt][] = prime[i];
            while (tmp % prime[i] == ) {
                factor[fatCnt][]++;
                tmp /= prime[i];
            }
            fatCnt++;
        }
    }
    if (tmp != ) {
        factor[fatCnt][] = tmp;
        factor[fatCnt++][] = ;
    }
    return fatCnt;
}
int main() {
    //相关操作......

    return ;
}