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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <limits.h>
  4.  
  5. int *primes, tblSize = 10, idx = 0, n = 2, maxFrom, maxStep, maxLength = 0;
  6.  
  7. void makePrimes();
  8.  
  9. void makePrimes()
  10. {
  11.   int i, j;
  12.   for (i = primes[idx - 1] + 2; i < INT_MAX / 10; i += 2) {
  13.     for ( j = 0; (i % primes[j]) && (i > primes[j]*primes[j]); ++j);
  14.     if (i % primes[j])
  15.       primes[idx++] = i;
  16.     if (idx == tblSize) {
  17.       tblSize *= 2;
  18.       primes = (int *)realloc(primes, sizeof(int) * tblSize);
  19.       if (primes == NULL) {
  20.         printf("prime table size expanded error\n");
  21.         exit(0);
  22.       } else {
  23.         printf("prime table size expanded to %d\n", tblSize);
  24.       }
  25.     }
  26.   }
  27. }
  28.  
  29. int seqLen(int i, int j)
  30. {
  31.   int len = 2;
  32.   int step = primes[j] - primes[i];
  33.   int n = primes[j] + step;
  34.   while (1) {
  35.     while (n > primes[j])j++;
  36.     if (n == primes[j]) {
  37.       len++;
  38.       n += step;
  39.     } else break;
  40.   }
  41.   return len;
  42. }
  43.  
  44. int main(void)
  45. {
  46.   int i, j, t;
  47.   primes = (int *)malloc(sizeof(int) * tblSize);
  48.   primes[idx++] = 2;
  49.   primes[idx++] = 3;
  50.   makePrimes();
  51.   printf("number of primes = %d\n", idx);
  52.   printf("calculating...\n");
  53.   for ( i = 0; i < idx; ++i) {
  54.     for ( j = i + 1; j  < idx; ++j  ) {
  55.       t = seqLen(i, j);
  56.       // printf("i j = %d %d %d\n", i,j,t);
  57.       if (maxLength < t) {
  58.         maxFrom = primes[i];
  59.         maxStep = primes[j] - primes[i];
  60.         maxLength = t;
  61.         printf("from step length = %d %d %d\n", maxFrom, maxStep, maxLength);
  62.       }
  63.     }
  64.   }
  65.   // printf("from step length = %d %d %d\n", maxFrom, maxStep, maxLength);
  66.  
  67.   return 0;
  68. }
  69.  
Time limit exceeded #stdin #stdout 5s 4372KB
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https://ideone.com/wHkuu3
language:
C (gcc 8.3)
created:
11 years ago
visibility:
secret

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