HDU-2136(素数筛选)

Largest prime factor

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 15836    Accepted Submission(s): 5507

Problem Description

Everybody knows any number can be combined by the prime number.
Now, your task is telling me what position of the largest prime factor.
The position of prime 2 is 1, prime 3 is 2, and prime 5 is 3, etc.
Specially, LPF(1) = 0.

 

Input

Each line will contain one integer n(0 < n < 1000000).

 

Output

Output the LPF(n).

 

Sample Input

12345

 

Sample Output

01213

 

Author

Wiskey

• AC Code

  #include 
  #include 
  using namespace std;
  
  int a[1000000];
  void init()
  {
      int k=1;        			//位置从1开始 
      for(int i=2; i<1000000; i++)
      {
          if(!a[i])
          {
              a[i]=k;
              for(int j=i*2; j<1000000; j=j+i)
              {
              	 a[j]=k;
              } 
              k++;
          }
      }
  }
  int main()
  {
      init();
      long long n;
      while(~scanf("%lld",&n))
      {
      	printf("%d\n",a[n]);
      }
      return 0;
  }