Improve solution of problem 18

C/p018.c

@@ -1,14 +1,41 @@
+/* By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum total from top to bottom is 23.
+ *    
+ *    3
+ *   7 4
+ *  2 4 6
+ * 8 5 9 3
+ *
+ * That is, 3 + 7 + 4 + 9 = 23.
+ *
+ * Find the maximum total from top to bottom of the triangle below:
+ *
+ *               75
+ *              95 64
+ *             17 47 82
+ *            18 35 87 10
+ *           20 04 82 47 65
+ *          19 01 23 75 03 34
+ *         88 02 77 73 07 63 67
+ *        99 65 04 28 06 16 70 92
+ *       41 41 26 56 83 40 80 70 33
+ *      41 48 72 33 47 32 37 16 94 29
+ *     53 71 44 65 25 43 91 52 97 51 14
+ *    70 11 33 28 77 73 17 78 39 68 17 57
+ *   91 71 52 38 17 14 91 43 58 50 27 29 48
+ *  63 66 04 68 89 53 67 30 73 16 69 87 40 31
+ * 04 62 98 27 23 09 70 98 73 93 38 53 60 04 23
+ *
+ * NOTE: As there are only 16384 routes, it is possible to solve this problem by trying every route. However, Problem 67, is the same challenge 
+ * with a triangle containing one-hundred rows; it cannot be solved by brute force, and requires a clever method! ;o)*/
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
-
-void sum_triangle(int **triang, int n, int i, int j, int sum);
-
-int max = 0; 
+#include "projecteuler.h"
 
 int main(int argc, char **argv)
 {
-   int i, j;
+   int i, j, max;
    int **triang;
    double elapsed;
    FILE *fp;
@@ -47,7 +74,7 @@ int main(int argc, char **argv)
 
    fclose(fp);
 
-   sum_triangle(triang, 15, 0, 0, 0);
+   max = find_max_path(triang, 15);
 
    clock_gettime(CLOCK_MONOTONIC, &end);
 
@@ -60,19 +87,3 @@ int main(int argc, char **argv)
 
    return 0;
 }
-
-void sum_triangle(int **triang, int n, int i, int j, int sum)
-{
-   if(i == n)
-   {
-      if(sum > max)
-      {
-         max = sum;
-      }
-      return;
-   }
-
-   sum_triangle(triang, n, i+1, j, sum+triang[i][j]);
-   sum_triangle(triang, n, i+1, j+1, sum+triang[i][j]);
-
-}

C/projecteuler.c

@@ -188,6 +188,24 @@ int count_divisors(int n)
    return count;
 }
 
+int find_max_path(int **triang, int n)
+{
+   int i, j;
+
+   for(i = n - 2; i >= 0; i--)
+   {
+      for(j = 0; j <= i; j++)
+      {
+         if(triang[i+1][j] > triang[i+1][j+1])
+            triang[i][j] += triang[i+1][j];
+         else
+            triang[i][j] += triang[i+1][j+1];
+      }
+   }
+
+   return triang[0][0];
+}
+
 void insertion_sort(void **array, int l, int r, int (*cmp)(void *lv, void *rv))
 {
    int i, j;

C/projecteuler.h

@@ -8,6 +8,7 @@ long int lcm(long int a, long int b);
 long int lcmm(long int *values, int n);
 int *sieve(int n);
 int count_divisors(int n);
+int find_max_path(int **triang, int n);
 void insertion_sort(void **array, int l, int r, int (*cmp)(void *lv, void *rv));
 void quick_sort(void **array, int l, int r, int (*cmp)(void *lv, void *rv));
 int is_pandigital(int value, int n);