54 lines
1012 B
C
54 lines
1012 B
C
#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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int collatz_length(long int n);
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int collatz_found[1000000] = {0};
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int main(int argc, char **argv)
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{
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int i, count, max = 0, max_l = 0;
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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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for(i = 1; i< 1000000; i++)
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{
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count = collatz_length(i);
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collatz_found[i] = count;
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if(count > max_l)
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{
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max_l = count;
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max = i;
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}
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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 14\n");
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printf("Answer: %d\n", max);
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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 collatz_length(long int n)
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{
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if(n == 1)
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return 1;
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if(n < 1000000 && collatz_found[n])
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return collatz_found[n];
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if(n % 2 == 0)
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return 1 + collatz_length(n/2);
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else
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return 1 + collatz_length(3*n+1);
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}
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