aoc2019/intcode/day2.c

//
// Created by red on 02/12/19.
//

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>

void print_elems(long* arr, size_t n);
long run(const long* input, size_t n, long noun, long verb);

int main() {
  char input_str[350];
  memset(input_str, 0, 350*sizeof(char));
  scanf("%s", input_str);
  long input[140];
  char* ptr = input_str;
  size_t i = 0;
  while (*ptr != 0) { //read until null
    input[i] = strtol(ptr, &ptr, 10);
    i++;
    ptr++; //skip the separator character (',')
  }
  size_t size = i;
  long out = run(input, size, 12, 2);
  printf("Value of mem[0] with noun=12, verb=2: %ld\n", out);
  //try noun=0..99, verb=0..99
  for (i = 0; i < 100; i++) {
    for (long j = 0; j < 100; j++) {
      long out = run(input, size, i, j);
      if (out == 19690720) {
        printf("Noun+verb found! n: %ld, v: %ld\n", i, j);
        return EXIT_SUCCESS;
      }
    }
  }
}

/**
 * @brief run the Intcode state machine with given initial tape
 *
 * replace the values of mem[1] and mem[2] with noun and verb respectively before running
 *
 * @param input is a pointer to the tape
 * @param n is the memory allocated
 * @param noun replaces mem[1]
 * @param verb replaces mem[2]
 * @return
 */
long run(const long* input, size_t n, long noun, long verb) {
  long mem[n];
  memcpy((void*) mem, (const void*) input, n*sizeof(long));
  size_t ptr = 0;
  mem[1] = noun;
  mem[2] = verb;
  while (ptr < n) {
    long opcode = mem[ptr];
    if (opcode == 1) {
      long a = mem[ptr+1];
      long b = mem[ptr+2];
      long c = mem[ptr+3];
      mem[c] = mem[a] + mem[b];
      ptr += 4;
    } else if (opcode == 2) {
      long a = mem[ptr+1];
      long b = mem[ptr+2];
      long c = mem[ptr+3];
      mem[c] = mem[a] * mem[b];
      ptr += 4;
    } else if (opcode == 99) {
      return mem[0];
    } else break;
  }
  return -1;
}

void print_elems(long* arr, size_t n) {
  puts("Printing elements of array");
  for (size_t i = 0; i < n; i++) {
    printf("%ld ", arr[i]);
  }
  puts("");
}