49 lines
1.1 KiB
C
49 lines
1.1 KiB
C
/* n! means n × (n − 1) × ... × 3 × 2 × 1
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*
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* For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,
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* and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
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*
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* Find the sum of the digits in the number 100!*/
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#define _POSIX_C_SOURCE 199309L
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#include <gmp.h>
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int main(int argc, char **argv)
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{
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double elapsed;
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struct timespec start, end;
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mpz_t fact, r, sum;
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clock_gettime(CLOCK_MONOTONIC, &start);
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/* Calculate the factorial using the GMP Library and sum the digits.*/
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mpz_inits(fact, r, sum, NULL);
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mpz_fac_ui(fact, 100);
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mpz_set_ui(sum, 0);
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while(mpz_cmp_ui(fact, 0))
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{
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mpz_tdiv_qr_ui(fact, r, fact, 10);
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mpz_add(sum, sum, r);
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}
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clock_gettime(CLOCK_MONOTONIC, &end);
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elapsed = (end.tv_sec - start.tv_sec) + (double)(end.tv_nsec - start.tv_nsec) / 1000000000;
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printf("Project Euler, Problem 20\n");
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gmp_printf("Answer: %Zd\n", sum);
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printf("Elapsed time: %.9lf seconds\n", elapsed);
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mpz_clears(fact, r, sum, NULL);
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return 0;
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}
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