Made day 1 part 2 less shitty (C)

01/day1_2.c

@@ -4,39 +4,27 @@
 
 
 // Originally, I used hashsets for this, which refused to work for me.
-// I would then find out that the implementation I was using hashes based on the pointer, not the value, so I just wrote an O(n²) solution. yay.
-// I hate myself for this. Could implement an ordered list to get O(log n) instead of O(n) for isIn, but who cares at this point.
+// I would then find out that the implementation I was using hashes based on the pointer, not the value, so I just wrote a stupid lookup table.
 
-#define inputLength 1024000 // adjust to length of input file
-
-int isIn(int array[inputLength], int value) {
-    for (int i=0; i<inputLength; i++) {
-        if (array[i] == value) {
-            return 1;
-        }
-    }
-    return 0;
-}
+#define inputLength 1000000 // adjust expected length
 
 int main() {
     int position = 0;
     char line [10];
-    int positions [inputLength] = {[0 ... 1023999] = -9999999};
-    int currectLine = 0;
+    int positions [inputLength]; // all initialized to 0
 
     while (1) {
     FILE* inputFile = fopen("input", "r");
         while (fgets(line, sizeof(line), inputFile)) {
             position += strtol(line, NULL, 10);
-            if (isIn(positions, position) == 1) {
+            // Because of part 1, we know that the numbers are steadily increasing.
+            // Negative numbers are therefore skipped, as we know the repeated number to be positive.
+            if (position > 0 && positions[position] == 1) {
                 printf("%d\n", position);
                 return 0;
             }
-            positions[currectLine] = position;
-            currectLine++;
+            positions[position] = 1;
         }
     }
-
-    return 0;
 }