112 lines
2.4 KiB
C
112 lines
2.4 KiB
C
/* The nth term of the sequence of triangle numbers is given by, tn = ½n(n+1); so the first ten triangle numbers are:
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*
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* 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...
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*
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* By converting each letter in a word to a number corresponding to its alphabetical position and adding these values we form a word value.
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* For example, the word value for SKY is 19 + 11 + 25 = 55 = t10. If the word value is a triangle number then we shall call the word a triangle word.
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*
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* Using words.txt (right click and 'Save Link/Target As...'), a 16K text file containing nearly two-thousand common English words,
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* how many are triangle words?*/
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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 <string.h>
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#include <time.h>
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int is_triang(int n);
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int main(int argc, char **argv)
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{
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int i, j, n, len, value, count = 0;
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char *line, **words;
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double elapsed;
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FILE *fp;
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struct timespec start, end;
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clock_gettime(CLOCK_MONOTONIC, &start);
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if((fp = fopen("words.txt", "r")) == NULL)
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{
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fprintf(stderr, "Error while opening file %s\n", "words.txt");
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return 1;
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}
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fscanf(fp, "%ms", &line);
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fclose(fp);
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n = 1;
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len = strlen(line);
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/* Count the words.*/
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for(i = 0; i < len; i++)
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{
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if(line[i] == ',')
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{
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n++;
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}
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}
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if((words = (char **)malloc(n*sizeof(char *))) == 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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/* Save the words in an array of strings.*/
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words[0] = strtok(line, ",\"");
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for(i = 1; i < n; i++)
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{
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words[i] = strtok(NULL, ",\"");
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}
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/* For each word, calculate its value and check if it's a triangle number.*/
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for(i = 0; i < n; i++)
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{
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value = 0;
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len = strlen(words[i]);
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for(j = 0; j < len; j++)
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{
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value += (words[i][j] - 'A' + 1);
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}
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if(is_triang(value))
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{
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count++;
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}
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}
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free(line);
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free(words);
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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 42\n");
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printf("Answer: %d\n", count);
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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_triang(int n)
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{
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int i, j;
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for(i = 1, j = 1; j <= n; i++, j += i)
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{
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if(n == j)
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{
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return 1;
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}
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}
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return 0;
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}
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