Eric Wastl has created a series of holiday themed programming exercises over at Advent of Code and I thought it would be fun to post my solutions to these exercises now that they have all been released. I’ll be posting more of my solutions as I have time to write up my methodologies (and complete some of them).

The first set of puzzles involves Santa navigating an infinite high-rise building with and infinite basement. Santa is given instructions in the form of a string of parentheses which tell him to go up or down one floor.

Part 1 #

Problem #

Santa is trying to deliver presents in a large apartment building, but he can’t find the right floor - the directions he got are a little confusing. He starts on the ground floor (floor 0) and then follows the instructions one character at a time.

An opening parenthesis, (, means he should go up one floor, and a closing parenthesis, ), means he should go down one floor.

The apartment building is very tall, and the basement is very deep; he will never find the top or bottom floors.

Methodology #

Both of these solutions follow the same basic formula. First, I read in the input that I’ve saved in source/day1source.txt and assign it to a variable. Next, I create a variable to hold the value of the current floor. I then use a loop to loop through each character in the string. For each character I check if the instruction is to go up one floor and if it is, I increment the floor variable by 1, otherwise I decrement the floor variable by 1. When the loop completes going through all the characters, I print out the final floor variable value.

Solutions #

Node.js #

var fs = require("fs");

var source = fs.readFileSync("../source/day1source.txt").toString();
var end = source.length;
var floor = 1;
for (var i = 0; i < end; i++) {
  if (source.charAt(i) === "(") {
    floor++;
  } else {
    floor--;
  }
}
console.log("Santa ends up on floor " + floor);

Python #

filename = '../source/day1source.txt'

with open(filename) as f:
    source = [line.rstrip('\n') for line in open(filename)]

floor = 0

for line in source:
    for char in line:
        if char == '(':
            floor = floor + 1
        else:
            floor = floor - 1

print "Santa ends up on floor", floor

Part 2 #

Problem #

Now, given the same instructions, find the position of the first character that causes him to enter the basement (floor -1). The first character in the instructions has position 1, the second character has position 2, and so on.

Methodology #

To solve this, I modified my code to detect when the floor variable equals -1 and prints out the current position in the string.

Solutions #

Node.js #

var fs = require("fs");

var source = fs.readFileSync("../source/day1source.txt").toString();
var end = source.length;
var floor = 1;
for (var i = 0; i < end; i++) {
  if (source.charAt(i) === "(") {
    floor++;
  } else {
    floor--;
  }
  if (floor === -1) {
    console.log(
      "The character " + source.charAt(i) + " at position " + i + " sent santa to the basement."
    );
  }
}

Python #

filename = '../source/day1source.txt'

with open(filename) as f:
    source = [line.rstrip('\n') for line in open(filename)]

floor = 0
count = 0

for line in source:
    for char in line:
        if char == '(':
            floor = floor + 1
        else:
            floor = floor - 1
        count = count + 1
        if floor == -1:
            print "Santa enters the basement on instruction", count
            break