non-functional C proof-of-concept

2022/day20.c

@@ -0,0 +1,115 @@
+#include <stdio.h>
+// #define INPUT_LENGTH 5000
+#define INPUT_LENGTH 7
+#define DEC_KEY 811589153
+
+struct list_node {
+	struct list_node* prev;
+	struct list_node* next;
+	long value;
+};
+
+void mix_right(struct list_node* node, long amount) {
+	struct list_node* new_prev = node->next;
+	amount %= INPUT_LENGTH-1;
+	// Pop from position
+	node->prev->next = node->next;
+	node->next->prev = node->prev;
+	// Advance from original next to the new prev
+	for (int i = 1; i < amount; i++) {
+		new_prev = new_prev->next;
+	}
+	// Set node to have correct new links
+	node->prev = new_prev;
+	node->next = new_prev->next;
+	// Insert after new prev
+	new_prev->next = node;  // same as node->prev->next = node;
+	node->next->prev = node;
+}
+
+void mix_left(struct list_node* node, long amount) {
+	struct list_node* new_next = node->prev;
+	amount %= INPUT_LENGTH-1;
+	// Pop from position
+	node->prev->next = node->next;
+	node->next->prev = node->prev;
+	// Advance from original prev to the new next
+	for (int i = 1; i < amount; i++) {
+		new_next = new_next->prev;
+	}
+	// Set node to have correct new links
+	node->next = new_next;
+	node->prev = new_next->prev;
+	// Insert after new prev
+	new_next->prev = node;  // same as node->next->prev = node;
+	node->prev->next = node;
+}
+
+void mix(struct list_node* node) {
+	int amount = node->value;
+	if (amount > 0) {
+		mix_right(node, amount);
+	} else if (amount < 0) {
+		mix_left(node, -amount);
+	}  // Do nothing for 0
+}
+
+int main(int argc, char *argv[]) {
+	struct list_node code[INPUT_LENGTH];
+	struct list_node* zero;  // Keep track of this node for later
+	long coord_x, coord_y, coord_z;
+	// Initialize circular doubly-linked list links
+	code[0].prev = &code[INPUT_LENGTH-1];
+	code[0].next = &code[1];
+	for (int i = 1; i < INPUT_LENGTH-1; i++) {
+		code[i].prev = &code[i-1];
+		code[i].next = &code[i+1];
+	}
+	code[INPUT_LENGTH-1].prev = &code[INPUT_LENGTH-2];
+	code[INPUT_LENGTH-1].next = &code[0];
+
+	// Init sample
+	code[0].value = 1;
+	code[1].value = 2;
+	code[2].value = -3;
+	code[3].value = 3;
+	code[4].value = -2;
+	code[5].value = 0;
+	code[6].value = 4;
+	zero = &code[5];
+
+	// // Load input
+	// FILE *fp = fopen("input/20", "r");
+	// for (int i = 0; i < INPUT_LENGTH; i++) {
+	// 	fscanf(fp, "%ld", &code[i].value);
+	// 	if (code[i].value == 0) {
+	// 		zero = &code[i];
+	// 	}
+	// }
+	// fclose(fp);
+
+	// Part 2 execution
+	for (int i = 0; i < INPUT_LENGTH; i++) {
+		code[i].value = code[i].value * DEC_KEY;
+	}
+	for (int pass = 0; pass < 10; pass++) {
+		for (int i = 0; i < INPUT_LENGTH; i++) {
+			mix(&code[i]);
+		}
+		printf("Resulting chain from mix %d: ", pass);
+		for (int i = 0; i < 7; i++) {
+			printf("%ld ", zero->value);
+			zero = zero->next;
+		}
+		printf("\n");
+	}
+	// Get resulting coords
+	for (int i = 0; i < 1000; i++) {zero = zero->next;}
+	coord_x = zero->value;
+	for (int i = 0; i < 1000; i++) {zero = zero->next;}
+	coord_y = zero->value;
+	for (int i = 0; i < 1000; i++) {zero = zero->next;}
+	coord_z = zero->value;
+	printf("Part 2: coords (%ld, %ld, %ld) give sum %ld\n", coord_x, coord_y, coord_z, coord_x+coord_y+coord_z);
+	return 0;
+}