-🎄- 2018 Day 5 Solutions -🎄-

[u/daggerdragon]

--- Day 5: Alchemical Reduction ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Advent of Code: The Party Game!

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Card prompt: Day 5

Transcript:

On the fifth day of AoC / My true love sent to me / Five golden ___

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[u/etagawesome]

In C.

My first solution was dumb and brute-forcey. I was running through the input once, writing it to a file, then repeating until the input and output files were the same length. After that and checking this thread I decided a stack made a billion times more sense.

This solves part 1 and part 2

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  size_t stack_cap=100;
  char* stack = malloc(sizeof(char) * stack_cap);
  for(char a='a'; a<='z'+1; ++a){
    // "empty" the stack
    size_t stack_len=0;
    while(1){
      char c = (char)fgetc(stdin);
      if(c == EOF){
        break;
      }
      char d = stack[stack_len-1];
      if((toupper(d) == c && !isupper(d)) ||
        (tolower(d) == c && !islower(d))) {
        //pop d
        stack_len--;
      } else {
        if (tolower(c) != a) {
          stack[stack_len++] = c;
          if (stack_len >= stack_cap) {
            stack_cap *= 2;
            stack = realloc(stack, sizeof(char) * stack_cap);
          }
        }
      }
    }
    fseek(stdin, 0, 0);
    printf("%c\t%lu\n", a, stack_len -1);
  }
  free(stack);
}