3 files changed, 56 insertions(+), 42 deletions(-)

M src/016.c
M src/017.c
M src/018.c

@@ 19,5 19,5 @@ int power_digit_sum(int base, int power) {
 
 int main() {
     assert(power_digit_sum(2,15) == 26);
-    printf("015: %d\n", power_digit_sum(2,1000));
+    printf("016: %d\n", power_digit_sum(2,1000));
 }

@@ 87,5 87,5 @@ int main() {
     assert(number_letter_count(1000) == 11);
     assert(number_letter_count(342) == 23);
     assert(number_letter_count(115) == 20);
-    printf("016: %d\n", sum_letter_count_until_n(1000));
+    printf("017: %d\n", sum_letter_count_until_n(1000));
 }

@@ 1,51 1,65 @@
 #include <stdio.h>
-#include <stdlib.h>
-#include <assert.h>
-#include "lib/math.h"
-
-int triangle_path(int x, int y) {
-    if (x > y)
-        x = y;
-    return nth_triangular(y) + x;
-}
 
-int maximum_path_sum(int *triangle, size_t size) {
-    int i, path;
-    for(i=0; i<size; i++) {
-        path = triangle_path(i, i);
-        printf("%d %d\n", path, triangle[path]);
+#define MAX_SIZE 15
+
+int lastRow[MAX_SIZE] = {0};
+int currentRow[MAX_SIZE] = {0};
+
+// Process rows by collapsing them into the previous row
+void processRow(int count) {
+    int index, left, right;
+
+    for (index = 0; index <= count; index++) {
+        if (index == 0) {
+            currentRow[index] += lastRow[index];
+        } else if (index == count) {
+            currentRow[index] += lastRow[index - 1];
+        } else {
+            left = currentRow[index] + lastRow[index - 1];
+            right = currentRow[index] + lastRow[index];
+            currentRow[index] = (left > right) ? left : right;
+        }
+    }
+    for (index = 0; index <= count; index++) {
+        lastRow[index] = currentRow[index];
     }
-    return 0;
 }
 
+int main(void) {
+    int maxSum = 0;
+    int temp = 0;
+    int row_index = 0;
+    int i;
+    char c;
+    FILE *fp;
 
-void populate_triangle(int *triangle, char filename[]) {
-    FILE *file = fopen(filename, "r");
-    if (file == NULL) {
-        printf("Failed to open file");
-        exit(1);
-    }
-    char c,digit[2];
-    int i = 0;
-    int digit_index = 0;
-    while ((c = fgetc(file)) != EOF) {
-        if (c == ' ' || c == '\n') {
-            triangle[i++] = atoi(digit);
-            digit_index = 0;
+    fp = fopen("src/resources/018_triangle.txt", "r");
+
+    while ((c = fgetc(fp)) != EOF) {
+        if (c == '\n') {
+            currentRow[row_index] = temp;
+            processRow(row_index);
+            temp = 0;
+            row_index = 0;
+        } else if (c == ' ') {
+            currentRow[row_index] = temp;
+            temp = 0;
+            row_index++;
         } else {
-            digit[digit_index++] = c;
+            /* Multiply current digit by ten. Since we are iterating one char
+               at the time we will receive a 7 and then a 5, so we need to turn
+               a 7 to 70 before adding 5 */
+            temp *= 10;
+            temp += (c - '0'); // convert ascii char to integer
         }
     }
-}
+    currentRow[row_index] = temp;
+    processRow(row_index);
 
-int main() {
-    assert(nth_triangular(4) == 10);
-    
-    int* triangle = calloc(nth_triangular(15),
-                           sizeof(int));
-    populate_triangle(triangle, "src/resources/018_triangle.txt");
-    maximum_path_sum(triangle, 3);
-    /* assert(maximum_path_sum(triangle, 3) == 393600); */
-    /* printf("018: %d\n", maximum_path_sum(triangle, 15)); */
-    free(triangle);
+    for (i=0; i<=MAX_SIZE; i++) {
+        if (maxSum < lastRow[i]) {
+            maxSum = lastRow[i];
+        }
+    }
+    printf("018: %d", maxSum);
 }