52 lines
1.3 KiB
C
52 lines
1.3 KiB
C
/* It is possible to write five as a sum in exactly six different ways:
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*
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* 4 + 1
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* 3 + 2
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* 3 + 1 + 1
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* 2 + 2 + 1
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* 2 + 1 + 1 + 1
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* 1 + 1 + 1 + 1 + 1
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*
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* How many different ways can one hundred be written as a sum of at least two positive integers?*/
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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 "projecteuler.h"
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int main(int argc, char **argv)
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{
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int n;
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long int *partitions;
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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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if((partitions = (long int *)calloc(100, sizeof(long int))) == NULL)
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{
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fprintf(stderr, "Error while allocating memory\n");
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return 1;
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}
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/* The number of ways a number can be written as a sum is given by the partition function
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* (-1 because the partition function includes also the number itself).
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* The function is implemented in projecteuler.c*/
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n = partition_fn(100, partitions, -1) - 1;
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free(partitions);
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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 76\n");
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printf("Answer: %d\n", n);
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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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