diff --git a/project_euler/Problem 08/sol1.c b/project_euler/Problem 08/sol1.c new file mode 100644 index 00000000..3577e3a0 --- /dev/null +++ b/project_euler/Problem 08/sol1.c @@ -0,0 +1,100 @@ +#include +#include + +int64_t get_product(FILE *fp, long start_pos, int num_digits) +{ + char ch = ' '; /* temporary variable to store character read from file */ + uint8_t num = 0; /* temporary variable to store digit read */ + int64_t prod = 1; /* product accumulator */ + int count = 0; /* we use this variable to count number of bytes of file read */ + + /* accumulate product for num_digits */ + for(int i = 0; i < num_digits; i++, count++) + { + /* get character from file */ + ch = getc(fp); + + /* the ASCII codes of digits is between 0x30 and 0x39. + * any character not in this range implies an invalid character + */ + if (ch < 0x30 || ch > 0x39) + { + if (ch == EOF) + return 0; + i--; + continue; + } + + num = ch - 0x30; /* convert character digit to number */ + if (num == 0) + { + /* If number is zero, we can skip the next 'num_digits' + * because this '0' will repeat in the next 'num_digit' multiplications. + * Hence, we also do not update the file position */ + /* NOTE: this is not needed but helps get results faster :) */ + return 0; + } + + prod *= num; /* accumulate product */ + } + + /* set file position to the next starting character + 1 */ + fseek(fp, -count + 1, SEEK_CUR); + + return prod; +} + + +int main(int argc, char* argv[]) +{ + int position = 0; + int num_digits = 4; + int64_t prod, max_prod = 0; + + /* if second command-line argument is ge=iven, + * use it as the number of digits to compute + * successive product for + */ + if (argc == 2) + num_digits = atoi(argv[1]); + + /* open file to read digits from */ + FILE *fp = fopen("digits.txt", "rt"); + if (!fp) + { + perror("Unable to open file"); + return -1; + } + + /* loop through all digits in the file */ + do + { + /* get product of 'num_digits' from current position in file */ + prod = get_product(fp, ftell(fp), num_digits); + + if (prod > max_prod) + { + max_prod = prod; + position = ftell(fp) - 1; + } + } while(!feof(fp)); /* loop till end of file is reached */ + + printf("Maximum product: %lld\t Location: %d^th position\n\t", max_prod, position); + fseek(fp, position, SEEK_SET); /* move cursor to identified position in file */ + /* loop through all digits */ + for (; num_digits > 0; num_digits--) + { + char ch = getc(fp); /* get character */ + /* skip invalid character */ + if (ch < 0x30 || ch > 0x39) + continue; + if (num_digits > 1) + printf("%c x ", ch); + else + printf("%c = %lld\n", ch, max_prod); + } + + fclose(fp); /* close file */ + + return 0; +}