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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <math.h>
  4.  
  5. #define NUM		600851475143
  6.  
  7. void sieve(int *table, int square);
  8.  
  9. int main(void)	{
  10.   int *table, square;
  11.   long long i;
  12.  
  13.   square = sqrt((double ) NUM);
  14.   table = (int *) malloc( ( square + 1 ) * sizeof(int));
  15.  
  16.   for(i = 0; i <= square; i++)
  17.     table[i] = 1;
  18.  
  19.   sieve(table, square);
  20.  
  21.   for(i = square; i >= 2; i--)	{
  22.     if( !(NUM % i) && table[i] == 1)	{
  23.       printf("%lld\n", i);
  24.       return 0;
  25.     }
  26.   }
  27.  
  28.   printf("\n");
  29.   return 0;
  30. }
  31.  
  32. void sieve(int *table, int square)
  33. {
  34.   int i, j;
  35.  
  36.   table[0] = table[1] = 0;
  37.  
  38.   for(i = 2; i <= square; i++)	{
  39.     for(j = 2 * i; j <= square; j += i)
  40.       table[j] = 0;
  41.   }
  42. }
Success #stdin #stdout 0.12s 4704KB
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https://ideone.com/db9jm
language:
C (gcc 8.3)
created:
13 years ago
visibility:
public

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