One-two primes: Difference between revisions
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=={{header|C}}==
{{trans|Wren}}
{{libheader|GMP}}
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <gmp.h>
void firstOneTwo(mpz_t res, int n) {
char *s;
bool found = false;
mpz_t k, r, m, t, one, nine;
mpz_inits(k, r, m, t, one, nine, NULL);
mpz_set_ui(one, 1);
mpz_set_ui(nine, 9);
mpz_set_ui(k, 10);
mpz_pow_ui(k, k, n);
mpz_sub_ui(k, k, 1);
mpz_tdiv_q(k, k, nine);
mpz_mul_2exp(r, one, n);
mpz_sub_ui(r, r, 1);
while (mpz_cmp(m, r) <= 0) {
s = mpz_get_str(NULL, 2, m);
mpz_set_str(t, s, 10);
mpz_add(t, k, t);
if (mpz_probab_prime_p(t, 15) > 0) {
found = true;
break;
}
mpz_add_ui(m, m, 1);
}
if (!found) mpz_set_si(t, -1);
mpz_set(res, t);
mpz_clears(k, r, m, t, one, nine, NULL);
}
int main() {
int n, ix;
char *s;
mpz_t res;
mpz_init(res);
for (n = 1; n < 21; ++n) {
firstOneTwo(res, n);
gmp_printf("%4d: %Zd\n", n, res);
}
for (n = 100; n <= 2000; n += 100) {
firstOneTwo(res, n);
if (!mpz_cmp_si(res, -1)) {
printf("No %d-digit prime found with only digits 1 or 2.", n);
} else {
s = mpz_get_str(NULL, 10, res);
ix = strchr(s, '2') - s;
printf("%4d: (1 x %4d) %s\n", n, ix, s + ix);
}
}
mpz_clear(res);
return 0;
}</syntaxhighlight>
{{out}}
<pre>
Same as Wren example.
</pre>
=={{header|J}}==
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