77 lines
1.6 KiB
C
77 lines
1.6 KiB
C
/* It can be seen that the number, 125874, and its double, 251748, contain exactly the same digits, but in a different order.
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*
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* Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits.*/
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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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int is_permutation(int a, int b);
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int main(int argc, char **argv)
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{
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int i;
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double elapsed;
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struct timespec start, end;
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clock_gettime(CLOCK_MONOTONIC, &start);
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i = 1;
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/* Brute force approach, try every integer number until the desired one is found.*/
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while(1)
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{
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if(is_permutation(i, 2*i) && is_permutation(i, 3*i) && is_permutation(i, 4*i) &&
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is_permutation(i, 5*i) && is_permutation(i, 6*i))
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{
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break;
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}
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i++;
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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 52\n");
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printf("Answer: %d\n", i);
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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_permutation(int a, int b)
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{
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int i;
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int digits1[10] = {0}, digits2[10] = {0};
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/* Get digits of a.*/
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while(a > 0)
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{
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digits1[a%10]++;
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a /= 10;
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}
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/* Get digits of b.*/
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while(b > 0)
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{
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digits2[b%10]++;
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b /= 10;
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}
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/* If they're not the same, return 0.*/
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for(i = 0; i < 10; i++)
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{
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if(digits1[i] != digits2[i])
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{
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return 0;
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}
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}
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return 1;
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}
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