1059 Prime Factors（25 分）(C++)

Given any positive integer N, you are supposed to find all of its prime factors, and write them in the format N = p​1​​​k​1​​​​×p​2​​​k​2​​​​×⋯×p​m​​​k​m​​​​.

Input Specification:

Each input file contains one test case which gives a positive integer N in the range of long int.

Output Specification:

Factor N in the format N = p​1​​^k​1​​*p​2​​^k​2​​*…*p​m​​^k​m​​, where p​i​​'s are prime factors of N in increasing order, and the exponent k​i​​ is the number of p​i​​ -- hence when there is only one p​i​​, k​i​​ is 1 and must NOT be printed out.

Sample Input:

97532468

Sample Output:

97532468=2^2*11*17*101*1291

题目大意：将一个数分解为若干素数之积；

解题思路：建立素数表

#include 
#include 
using namespace std;
int x;
vectorisprime(500000,true);
int main(){
    int i,j,cnt=1;
    bool flag=true;
    for(i=2;i<5000;i++)
        for(j=i*i;j<500000;j+=i)
            isprime[j]=false;
    cin>>x;
    printf("%d=",x);
    if(x==1)
      cout<<1;
    while(x>1){
        cnt++;
        while(isprime[cnt]==false)
            cnt++;
        int num=0;
        while(x%cnt==0){
            x/=cnt;
            num++;
        }
        if(num>=1){
            if(flag==false)
                printf("*");
            printf("%d",cnt);
            if(num>1)
                printf("^%d",num);
            flag=false;
        }
    }
}