documented remaining project euler programs

project_euler/problem_12/sol1.c

@@ -1,6 +1,6 @@
 /**
  * \file
- * \brief [Problem 11](https://projecteuler.net/problem=11) solution
+ * \brief [Problem 12](https://projecteuler.net/problem=12) solution
  */
 #include <math.h>
 #include <stdio.h>

project_euler/problem_13/sol1.c

@@ -1,11 +1,15 @@
+/**
+ * \file
+ * \brief [Problem 13](https://projecteuler.net/problem=13) solution
+ */
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-/* Function to read the number from a file and store it in array.
-    index 0 of output buffer => units place
-    index 1 of output buffer => tens place and so on
+/** Function to read the number from a file and store it in array.
+    \n index 0 of output buffer => units place
+    \n index 1 of output buffer => tens place and so on
     i.e., index i => 10^i th place
  */
 int get_number(FILE *fp, char *buffer, uint8_t *out_int)
@@ -73,6 +77,7 @@ int add_numbers(uint8_t *a, uint8_t *b, uint8_t N)
     return 0;
 }
 
+/** Function to print a long number */
 int print_number(uint8_t *number, uint8_t N, int8_t num_digits_to_print)
 {
     uint8_t start_pos = N - 1;
@@ -101,9 +106,12 @@ int print_number(uint8_t *number, uint8_t N, int8_t num_digits_to_print)
     return 0;
 }
 
+/** number of digits of the large number */
 #define N 10
+/** number of digits in output number */
 #define N2 (N + 10)
 
+/** Main function */
 int main(void)
 {
     // const char N = 50, N2 = N+10;          /* length of numbers */
@@ -139,4 +147,4 @@ int main(void)
 
     fclose(fp); /* close file */
     return 0;
-}
+}

project_euler/problem_14/sol1.c

@@ -1,6 +1,20 @@
+/**
+ * \file
+ * \brief [Problem 14](https://projecteuler.net/problem=14) solution
+ *
+ * Since the computational values for each iteration step are independent,
+ * we can compute them in parallel. However, the maximum values should be
+ * updated in synchrony so that we do not get into a "race condition".
+ *
+ * To compile with supporintg gcc or clang, the flag "-fopenmp" should be
+ * passes while with Microsoft C compiler, the flag "/fopenmp" should be
+ * used. If you are using the provided CMAKE compilation, it will automatically
+ * detect OPENMP and compile with it for you.
+ *
+ * Automatically detects for OPENMP using the _OPENMP macro.
+ */
 #include <stdio.h>
 #include <stdlib.h>
-
 #ifdef _OPENMP
 #include <omp.h>
 #endif
@@ -25,6 +39,7 @@ long long collatz(long long start_num)
     return length;
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     long long max_len = 0, max_len_num = 0;
@@ -37,17 +52,6 @@ int main(int argc, char **argv)
         printf("Maximum number: %lld\n", MAX_NUM);
     }
 
-    /**
-     * Since the computational values for each iteration step are independent,
-     * we can compute them in parallel. However, the maximum values should be
-     * updated in synchrony so that we do not get into a "race condition".
-     *
-     * To compile with supporintg gcc or clang, the flag "-fopenmp" should be
-     *passes while with Microsoft C compiler, the flag "/fopenmp" should be
-     *used.
-     *
-     * Automatically detects for OPENMP using the _OPENMP macro.
-     **/
     long long i;
 #ifdef _OPENMP
 #pragma omp parallel for shared(max_len, max_len_num) schedule(guided)
@@ -71,4 +75,4 @@ int main(int argc, char **argv)
     printf("Start: %3lld: \tLength: %5lld\n", max_len_num, max_len);
 
     return 0;
-}
+}

project_euler/problem_15/sol1.c

@@ -1,3 +1,7 @@
+/**
+ * \file
+ * \brief [Problem 15](https://projecteuler.net/problem=15) solution
+ */
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -21,6 +25,7 @@ unsigned long long number_of_paths(int N)
     return path;
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     int N = 20;
@@ -32,4 +37,4 @@ int main(int argc, char **argv)
            number_of_paths(N));
 
     return 0;
-}
+}

project_euler/problem_16/sol1.c

@@ -1,8 +1,13 @@
+/**
+ * \file
+ * \brief [Problem 16](https://projecteuler.net/problem=16) solution
+ */
 #include <math.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 
+/** Main function */
 int main(int argc, char **argv)
 {
     const double tmp = log(10) / log(2); /* required to get number of digits */
@@ -54,4 +59,4 @@ int main(int argc, char **argv)
 
     free(digits);
     return 0;
-}
+}

project_euler/problem_19/sol1.c

@@ -1,9 +1,13 @@
+/**
+ * \file
+ * \brief [Problem 19](https://projecteuler.net/problem=19) solution
+ */
 #include <stdio.h>
 
 /**
  * returns number of days in a month.
- * Month is identified by an integer -
- * 0 = Jan and 11 = December
+ * Month is identified by an integer -\n
+ * > 0 = Jan and 11 = December\n
  * For February, adjust for leap year outside the function.
  **/
 char get_month_days(short month)
@@ -42,6 +46,7 @@ char is_leap_year(short year)
 }
 
 #ifdef DEBUG
+/** Function to convert integer month to string */
 const char *day_string(int day)
 {
     switch (day)
@@ -66,6 +71,7 @@ const char *day_string(int day)
 }
 #endif
 
+/** Main function */
 int main(int argc, char **argv)
 {
     int count_sundays = 0;
@@ -120,4 +126,4 @@ int main(int argc, char **argv)
            count_sundays);
 
     return 0;
-}
+}

project_euler/problem_20/sol1.c

@@ -1,3 +1,10 @@
+/**
+ * \file
+ * \brief [Problem 20](https://projecteuler.net/problem=20) solution
+ *
+ * Implementation uses a custom `big_int` structure that can store arbitrarilty
+ * large integer numbers.
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -14,6 +21,7 @@ typedef struct _big_int
 } big_int;
 
 #ifdef DEBUG
+/** print a digit from large integer */
 void print_digit(const big_int *my_int)
 {
     printf("\tValue : %d\n\tNext : %p\n\tPrev : %p\n", my_int->value,
@@ -82,6 +90,7 @@ char remove_digits(big_int *digit, int N)
     return remove_digits(digit->next_digit, 0);
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     unsigned int N = 5;

project_euler/problem_21/sol1.c

@@ -1,34 +1,29 @@
+/**
+ * \file
+ * \brief [Problem 21](https://projecteuler.net/problem=21) solution
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
-#ifdef _OPENMP
-#include <omp.h>
-#endif
 
 /**
  * function to return the sum of proper divisors of N
  **/
-unsigned int sum_of_divisors(unsigned int N)
+unsigned long sum_of_divisors(unsigned int N)
 {
-    unsigned int sum = 1; /* 1 is always a divisor */
-
+    unsigned long sum = 1 + N; /* 1 and itself are always a divisor */
     /* divisors are symmertically distributed about the square-root */
-    for (unsigned int i = 2; (i * i) <= N; i++)
+    for (unsigned int i = 2; i * i < N; i++)
     {
-        if (N % i != 0)
-            /* i is not a proper divisor */
+        if ((N % i) != 0)
+            /* i is not a divisor of N */
             continue;
 
         // #ifdef DEBUG
         //         printf("%4d, %4d,", i, N / i);
         // #endif
 
-        sum += i;
-
-        if (i * i == N)
-            continue;
-
-        sum += N / i;
+        sum += i + (N / i);
     }
     // #ifdef DEBUG
     //     printf("\nSum of divisors of %4d: %4d\n", N, sum);
@@ -36,6 +31,7 @@ unsigned int sum_of_divisors(unsigned int N)
     return sum;
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     unsigned long sum = 0;
@@ -43,7 +39,7 @@ int main(int argc, char **argv)
     if (argc == 2)
         MAX_N = atoi(argv[1]);
 
-    /**
+    /**<
      * We use an array of flags to check if a number at the index was:
      * not-processed = 0
      * is amicable = 1
@@ -53,9 +49,6 @@ int main(int argc, char **argv)
 
     clock_t start_time = clock();
     int i;
-#ifdef _OPENMP
-#pragma omp for schedule(runtime)
-#endif
     /* there are no such numbers till 10. Lets search from there on */
     for (i = 10; i < MAX_N; i++)
     {

project_euler/problem_22/sol1.c

@@ -1,3 +1,7 @@
+/**
+ * \file
+ * \brief [Problem 22](https://projecteuler.net/problem=22) solution
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -6,8 +10,8 @@
 #include <omp.h>
 #endif
 
-#define MAX_NAMES 6000  /* Maximum number of names to store */
-#define MAX_NAME_LEN 20 /* Maximum length of each name */
+#define MAX_NAMES 6000  /**< Maximum number of names to store */
+#define MAX_NAME_LEN 20 /**< Maximum length of each name */
 
 /**
  * Alphabetical sorting using 'shell sort' algorithm
@@ -63,6 +67,7 @@ void lazy_sort(char data[][MAX_NAME_LEN], int LEN)
 #endif
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     unsigned long COUNT = 0;
@@ -80,9 +85,9 @@ int main(int argc, char **argv)
         return -1;
     }
 
-    /**
+    /*
      * Loops to get total number of rows and columns in the file
-     **/
+     */
     do
     {
         int ret = fscanf(fp, "\"%[^\",]\",", names[COUNT++]);

project_euler/problem_23/sol1.c

@@ -1,3 +1,7 @@
+/**
+ * \file
+ * \brief [Problem 23](https://projecteuler.net/problem=23) solution
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -5,7 +9,7 @@
 #include <omp.h>
 #endif
 
-unsigned long MAX_N = 28123;
+unsigned long MAX_N = 28123; /**< upper limit of numbers to check */
 
 /**
  * Returns:
@@ -58,8 +62,8 @@ unsigned long get_next_abundant(unsigned long N)
 /**
  * check if a given number can be represented as a sum
  * of two abundant numbers.
- * 1 - if yes
- * 0 - if not
+ * \returns 1 - if yes
+ * \returns 0 - if not
  **/
 char is_sum_of_abundant(unsigned long N)
 {
@@ -79,6 +83,7 @@ char is_sum_of_abundant(unsigned long N)
     return 0;
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     unsigned long sum = 0;

project_euler/problem_23/sol2.c

@@ -1,4 +1,11 @@
-
+/**
+ * \file
+ * \brief [Problem 23](https://projecteuler.net/problem=23) solution -
+ * optimization using look-up array
+ *
+ * Optimization applied - compute & store abundant numbers once
+ * into a look-up array.
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -6,12 +13,7 @@
 #include <omp.h>
 #endif
 
-/**
- * Optimization 1 - compute & store abundant numbers once
- * into a look-up array
- **/
-
-long MAX_N = 28123;
+long MAX_N = 28123; /**< Limit of numbers to check */
 
 /**
  * This is the global array to be used to store a flag to identify
@@ -77,8 +79,8 @@ unsigned long get_next_abundant(unsigned long N)
 /**
  * check if a given number can be represented as a sum
  * of two abundant numbers.
- * 1 - if yes
- * 0 - if not
+ * \returns 1 - if yes
+ * \returns 0 - if not
  **/
 char is_sum_of_abundant(unsigned long N)
 {
@@ -98,6 +100,7 @@ char is_sum_of_abundant(unsigned long N)
     return 0;
 }
 
+/** Main function */
 int main(int argc, char **argv)
 {
     unsigned long sum = 0;

project_euler/problem_25/sol1.c

@@ -1,13 +1,18 @@
+/**
+ * \file
+ * \brief [Problem 25](https://projecteuler.net/problem=25) solution implemented
+ * using arbitrarily large numbers represented as arrays
+ */
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
 
-#define MAX_DIGITS 1000
+#define MAX_DIGITS 1000 /**< maximum number of digits */
 
 /**
- * Function to add arbitraty length decimal integers stored in an array.
+ * Function to add arbitraty length decimal integers stored in an array.\n
  * a + b = c = new b
  **/
 unsigned int add_numbers(unsigned char *a, unsigned char *b, unsigned char *c,
@@ -48,6 +53,7 @@ unsigned int add_numbers(unsigned char *a, unsigned char *b, unsigned char *c,
     return i;
 }
 
+/** Print a large number */
 int print_number(unsigned char *number, int N)
 {
     int start_pos = N - 1;
@@ -62,6 +68,7 @@ int print_number(unsigned char *number, int N)
     return 0;
 }
 
+/** Get number of digits in a large number */
 unsigned int get_digits(unsigned char *number)
 {
     unsigned int digits = MAX_DIGITS;
@@ -70,6 +77,7 @@ unsigned int get_digits(unsigned char *number)
     return digits;
 }
 
+/** Main function */
 int main(int argc, char *argv[])
 {
     unsigned char

project_euler/problem_26/sol1.c

@@ -1,3 +1,7 @@
+/**
+ * \file
+ * \brief [Problem 26](https://projecteuler.net/problem=26) solution
+ */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -6,14 +10,17 @@
 #include <omp.h>
 #endif
 
-#define MAX_DENO 2000
-#define MAX_LEN (MAX_DENO + 10)
+#define MAX_DENO 2000 /**< limit of unit fractions */
+#define MAX_LEN                                                                \
+    (MAX_DENO + 10) /**< length of resulting recurring fraction number */
 
+/** comparison function for use with internal `qsort` algorithm */
 int compare(const void *a, const void *b)
 {
     return (*(unsigned short *)a - *(unsigned short *)b);
 }
 
+/** Main function */
 int main(int argc, char *argv[])
 {
     unsigned short max_digits = 0, max_idx_number = 0;