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HDU 5108Alexandra and Prime Numbers(大素数)
Problem Description
Alexandra has a little brother. He is new to programming. One day he is solving the following problem: Given an positive integer N, judge whether N is prime.
The problem above is quite easy, so Alexandra gave him a new task: Given a positive integer N, find the minimal positive integer M, such that N/M is prime. If such M doesn‘t exist, output 0.
Help him!
The problem above is quite easy, so Alexandra gave him a new task: Given a positive integer N, find the minimal positive integer M, such that N/M is prime. If such M doesn‘t exist, output 0.
Help him!
Input
There are multiple test cases (no more than 1,000). Each case contains only one positive integer N.
N≤1,000,000,000 .
Number of cases withN>1,000,000 is no more than 100.
Number of cases with
Output
For each case, output the requested M, or output 0 if no solution exists.
Sample Input
3 4 5 6
Sample Output
1 2 1 2
对于此题,我只想说自己好傻的,对于一个大数n,求最小的m是的n/m是素数
首先 n=素数*素数*素数......
那么我们求最大的素数,还有这个素数中不可能有两个大于sqrt(n)的,那么代码如下
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #include<queue> #include<cmath> #define L(x) (x<<1) #define R(x) (x<<1|1) #define MID(x,y) ((x+y)>>1) using namespace std; typedef __int64 ll; #define N 100000 ll a[N],b[N]; ll k; void inset() { int i,j; a[0]=1; for(i=2;i<N;i++) if(!a[i]) { for(j=i*2;j<N;j+=i) a[j]=1; b[k++]=i; } } int main() { int i,j; inset(); ll n,temp; while(~scanf("%I64d",&n)) { if(n==1) { printf("0\n"); continue; } int flag=0; temp=n; ll m=(ll)(sqrt(n))+1; ll ans=0; for(m;m>1;m--) if(n%m==0) { while(n%m==0&&!a[m]) n/=m; if(!a[m]) { ans=max(ans,m); } } ans=(ll)max(ans,n); printf("%I64d\n",temp/ans); } return 0; }
HDU 5108Alexandra and Prime Numbers(大素数)
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