solve day 21
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day21.c
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241
day21.c
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#include <stdio.h>
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#include <assert.h>
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#include <string.h>
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#include "types.h"
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#include "aoc.h"
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#define DAY21_MAX_MONKEYS 1048575 // 2^20-1
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typedef enum {
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MONKEY21_OP_CONST,
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MONKEY21_OP_ADD,
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MONKEY21_OP_SUB,
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MONKEY21_OP_DIV,
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MONKEY21_OP_MUL,
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} day21_monkey_op;
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typedef struct {
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char name[5]; // null-terminated
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day21_monkey_op op;
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i32 constant;
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char monkey1[5]; // null-terminated
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char monkey2[5]; // null-terminated
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} day21_monkey;
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typedef struct {
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day21_monkey *monkeys;
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u32 count;
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} day21_data;
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static void* day21_parse(char** lines, int line_count)
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{
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day21_data *data = malloc(sizeof(day21_data));
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data->monkeys = calloc(line_count, sizeof(day21_monkey));
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data->count = line_count;
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for (int i = 0; i < line_count; i++) {
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day21_monkey *monkey = &data->monkeys[i];
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char *line = lines[i];
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strncpy(monkey->name, line, sizeof(monkey->name)-1);
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char *after_colon = line+6;
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char *sep;
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if ((sep = strchr(after_colon, '+'))) {
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monkey->op = MONKEY21_OP_ADD;
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strncpy(monkey->monkey1, after_colon , sizeof(monkey->monkey1)-1);
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strncpy(monkey->monkey2, after_colon+7, sizeof(monkey->monkey2)-1);
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} else if ((sep = strchr(after_colon, '-'))) {
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monkey->op = MONKEY21_OP_SUB;
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strncpy(monkey->monkey1, after_colon , sizeof(monkey->monkey1)-1);
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strncpy(monkey->monkey2, after_colon+7, sizeof(monkey->monkey2)-1);
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} else if ((sep = strchr(after_colon, '*'))) {
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monkey->op = MONKEY21_OP_MUL;
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strncpy(monkey->monkey1, after_colon , sizeof(monkey->monkey1)-1);
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strncpy(monkey->monkey2, after_colon+7, sizeof(monkey->monkey2)-1);
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} else if ((sep = strchr(after_colon, '/'))) {
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monkey->op = MONKEY21_OP_DIV;
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strncpy(monkey->monkey1, after_colon , sizeof(monkey->monkey1)-1);
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strncpy(monkey->monkey2, after_colon+7, sizeof(monkey->monkey2)-1);
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} else {
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monkey->op = MONKEY21_OP_CONST;
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monkey->constant = strtol(after_colon, NULL, 10);
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}
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}
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return data;
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}
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static void day21_print_monkey(day21_monkey *monkey)
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{
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printf("%s: ", monkey->name);
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switch (monkey->op) {
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case MONKEY21_OP_CONST:
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printf("%d\n", monkey->constant);
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break;
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case MONKEY21_OP_ADD:
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printf("%s + %s\n", monkey->monkey1, monkey->monkey2);
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break;
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case MONKEY21_OP_SUB:
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printf("%s - %s\n", monkey->monkey1, monkey->monkey2);
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break;
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case MONKEY21_OP_DIV:
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printf("%s / %s\n", monkey->monkey1, monkey->monkey2);
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break;
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case MONKEY21_OP_MUL:
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printf("%s * %s\n", monkey->monkey1, monkey->monkey2);
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break;
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}
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}
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static u32 day21_monkey_key(char *name)
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{
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char c1 = name[0] - 'a';
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char c2 = name[1] - 'a';
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char c3 = name[2] - 'a';
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char c4 = name[3] - 'a';
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u32 key = (c4 << 15) | (c3 << 10) | (c2 << 5) | (c1 << 0);
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return key;
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}
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static day21_monkey *day21_monkey_by_name(day21_monkey *lut[DAY21_MAX_MONKEYS], char *name)
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{
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return lut[day21_monkey_key(name)];
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}
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static day21_monkey **day21_create_monkey_lookup(day21_monkey *monkeys, u32 count)
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{
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day21_monkey **monkey_lookup = calloc(DAY21_MAX_MONKEYS, sizeof(day21_monkey*));
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for (int i = 0; i < count; i++) {
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day21_monkey *monkey = &monkeys[i];
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u32 key = day21_monkey_key(monkey->name);
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assert(key <= DAY21_MAX_MONKEYS);
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assert(monkey_lookup[key] == NULL && "Key collision");
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monkey_lookup[key] = monkey;
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}
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return monkey_lookup;
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}
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static i64 day21_eval(day21_monkey *lut[DAY21_MAX_MONKEYS], char *name)
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{
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day21_monkey *monkey = day21_monkey_by_name(lut, name);
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switch(monkey->op) {
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case MONKEY21_OP_CONST: return monkey->constant;
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case MONKEY21_OP_ADD: return day21_eval(lut, monkey->monkey1) + day21_eval(lut, monkey->monkey2);
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case MONKEY21_OP_SUB: return day21_eval(lut, monkey->monkey1) - day21_eval(lut, monkey->monkey2);
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case MONKEY21_OP_DIV: return day21_eval(lut, monkey->monkey1) / day21_eval(lut, monkey->monkey2);
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case MONKEY21_OP_MUL: return day21_eval(lut, monkey->monkey1) * day21_eval(lut, monkey->monkey2);
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}
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}
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static void day21_part1(void *p)
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{
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day21_data *data = (day21_data*)p;
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day21_monkey **monkey_lookup = day21_create_monkey_lookup(data->monkeys, data->count);
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printf("%ld\n", day21_eval(monkey_lookup, "root"));
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}
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static bool day21_has_params(day21_monkey_op op)
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{
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return op == MONKEY21_OP_ADD || op == MONKEY21_OP_SUB || op == MONKEY21_OP_DIV || op == MONKEY21_OP_MUL;
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}
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static u32 day21_walk_to(day21_monkey *lut[DAY21_MAX_MONKEYS], day21_monkey *from, char *to, day21_monkey **chain)
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{
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if (day21_monkey_key(from->name) == day21_monkey_key(to)) {
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chain[0] = from;
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return 1;
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}
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if (!day21_has_params(from->op)) return 0;
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chain[0] = from;
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u32 chain_length;
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day21_monkey *monkey1 = day21_monkey_by_name(lut, from->monkey1);
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chain_length = day21_walk_to(lut, monkey1, to, chain+1);
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if (chain_length) {
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return chain_length+1;
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}
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day21_monkey *monkey2 = day21_monkey_by_name(lut, from->monkey2);
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chain_length = day21_walk_to(lut, monkey2, to, chain+1);
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if (chain_length) {
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return chain_length+1;
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}
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chain[0] = NULL;
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return 0;
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}
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static void day21_part2(void *p)
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{
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day21_data *data = (day21_data*)p;
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day21_monkey **lut = day21_create_monkey_lookup(data->monkeys, data->count);
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day21_monkey *root = day21_monkey_by_name(lut, "root");
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day21_monkey *chain[data->count];
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memset(chain, 0, sizeof(day21_monkey*) * data->count);
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u32 chain_length = day21_walk_to(lut, root, "humn", chain);
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if (chain_length == 0) {
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printf("Failed to find 'humn' monkey\n");
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return;
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}
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day21_monkey *curr;
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i64 expected;
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if (day21_monkey_key(root->monkey1) == day21_monkey_key(chain[1]->name)) {
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expected = day21_eval(lut, root->monkey2);
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curr = lut[day21_monkey_key(root->monkey1)];
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} else {
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expected = day21_eval(lut, root->monkey1);
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curr = lut[day21_monkey_key(root->monkey2)];
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}
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u32 chain_idx = 2;
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for (int chain_idx = 2; chain_idx < chain_length; chain_idx++) {
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u32 monkey1_key = day21_monkey_key(curr->monkey1);
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u32 monkey2_key = day21_monkey_key(curr->monkey2);
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bool is_humn_lhs = (monkey1_key == day21_monkey_key(chain[chain_idx]->name));
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day21_monkey *side_branch = lut[is_humn_lhs ? monkey2_key : monkey1_key];
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day21_monkey *humn_branch = lut[is_humn_lhs ? monkey1_key : monkey2_key];
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i64 side_value = day21_eval(lut, side_branch->name);
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switch (curr->op) {
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case MONKEY21_OP_ADD:
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expected = expected - side_value;
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break;
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case MONKEY21_OP_SUB:
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if (is_humn_lhs) {
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expected = expected + side_value;
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} else {
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expected = side_value - expected;
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}
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break;
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case MONKEY21_OP_MUL:
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expected = expected / side_value;
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break;
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case MONKEY21_OP_DIV:
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if (is_humn_lhs) {
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expected = expected * side_value;
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} else {
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expected = side_value / expected ;
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}
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break;
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case MONKEY21_OP_CONST:
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assert(false && "Should never happen");
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break;
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}
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curr = humn_branch;
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}
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printf("%ld\n", expected);
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}
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ADD_SOLUTION(21, day21_parse, day21_part1, day21_part2);
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