113 lines
2.5 KiB
C
113 lines
2.5 KiB
C
/* In the 5 by 5 matrix below, the minimal path sum from the top left to the bottom right, by only moving to the right and down,
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* is indicated in bold red and is equal to 2427.
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*
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* *131* 673 234 103 18
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* *201* *96* *342* 965 150
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* 630 803 *746* *422* 111
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* 537 699 497 *121* 956
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* 805 732 524 *37* *331*
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*
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* Find the minimal path sum, in matrix.txt, a 31K text file containing a 80 by 80 matrix, from the top left to the bottom right
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* by only moving right and down.*/
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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 <limits.h>
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int sum_paths(int **matrix, int m, int n);
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int main(int argc, char **argv)
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{
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int i, j, dist;
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int **matrix;
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double elapsed;
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struct timespec start, end;
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FILE *fp;
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clock_gettime(CLOCK_MONOTONIC, &start);
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if((fp = fopen("matrix.txt", "r")) == NULL)
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{
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fprintf(stderr, "Error while opening file %s\n", "matrix.txt");
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return 1;
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}
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if((matrix = (int **)malloc(80*sizeof(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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for(i = 0; i < 80; i++)
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{
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if((matrix[i] = (int *)malloc(80*sizeof(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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}
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for(i = 0; i < 80; i++)
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{
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for(j = 0; j < 80; j++)
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{
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fscanf(fp, "%d,", &matrix[i][j]);
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}
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}
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fclose(fp);
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dist = sum_paths(matrix, 80, 80);
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for(i = 0; i < 80; i++)
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{
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free(matrix[i]);
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}
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free(matrix);
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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 81\n");
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printf("Answer: %d\n", dist);
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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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/* Get the shortest path starting from the bottom right corner
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* and going backwards.*/
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int sum_paths(int **matrix, int m, int n)
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{
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int i, j;
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for(i = m - 2; i >= 0; i--)
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{
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matrix[m-1][i] += matrix[m-1][i+1];
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matrix[i][m-1] += matrix[i+1][m-1];
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}
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for(i = m - 2; i >= 0; i--)
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{
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for(j = n - 2; j >= 0; j--)
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{
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if(matrix[i][j+1] > matrix[i+1][j])
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{
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matrix[i][j] += matrix[i+1][j];
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}
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else
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{
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matrix[i][j] += matrix[i][j+1];
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}
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}
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}
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return matrix[0][0];
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}
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