83 lines
1.9 KiB
C
83 lines
1.9 KiB
C
/* It is well known that if the square root of a natural number is not an integer, then it is irrational.
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* The decimal expansion of such square roots is infinite without any repeating pattern at all.
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*
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* The square root of two is 1.41421356237309504880..., and the digital sum of the first one hundred decimal digits is 475.
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*
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* For the first one hundred natural numbers, find the total of the digital sums of the first one hundred decimal digits
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* for all the irrational square roots*/
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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 <math.h>
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#include <time.h>
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#include <gmp.h>
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int is_square(int n);
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int main(int argc, char **argv)
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{
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int i, j, sum = 0;
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char sqrt_digits[104];
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double elapsed;
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struct timespec start, end;
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mpf_t sqrt;
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clock_gettime(CLOCK_MONOTONIC, &start);
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/* Set the precision to 333 bits (should be enough for 100 decimal digits.*/
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mpf_set_default_prec(333);
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mpf_init(sqrt);
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for(i = 2; i < 100; i++)
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{
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if(is_square(i))
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{
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continue;
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}
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/* Calculate the square root of the current number with the given precision
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* and sum the digits to the total.*/
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mpf_sqrt_ui(sqrt, i);
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gmp_sprintf(sqrt_digits, "%.101Ff\n", sqrt);
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sum += (sqrt_digits[0] - '0');
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for(j = 2; j < 101; j++)
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{
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sum += (sqrt_digits[j] - '0');
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}
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}
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mpf_clear(sqrt);
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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 80\n");
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printf("Answer: %d\n", sum);
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printf("Elapsed time: %.9lf seconds\n", elapsed);
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return 0;
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}
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int is_square(int n)
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{
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int m;
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double p;
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p = sqrt(n);
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m = p;
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if(p == m)
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{
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return 1;
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}
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else
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{
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return 0;
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}
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}
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