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Robert Mion
Robert Mion

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#adventofcode #algorithms #programming #javascript

Advent of Code 2016 Day 2

Part 1

  1. Setting up the data structures
  2. A double-reduce()r to solve the puzzle

Setting up the data structures

My map for traversing the array based on the direction:

{
  'U': [-1,0],
  'R': [0,1],
  'D': [1,0],
  'L': [0,-1]
}
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My data structure for the keypad:

[
  [1,2,3],
  [4,5,6],
  [7,8,9]
]
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5 is at [1,1]

A double-reduce()r to solve the puzzle

The iteration portion of my algorithm in pseudocode:

For each line from the input
  Accumulate a code - starting as an empty string
  For each character in the line
    Accumulate a 2-element array of coordinates
    If the next location is a valid cell
      Return the coordinate of the next location
    Else
      Return the coordinate of the current location
  Add the value at the final cell to the string
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The iteration portion of my algorithm in JavaScript:

input.reduce(
  (code, line) => {
    key = line.reduce(
      (coords, path) => 
        keypad[coords[0] + map[path][0]] &&
        keypad[coords[0] + map[path][0]][coords[1] + map[path][1]]
        ? [ coords[0] + map[path][0],
            coords[1] + map[path][1] ]
        : coords,
        key.slice()
    )
    return code += keypad[key[0]][key[1]]
  }, ""
)
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Part 1: solved!

Part 2

Three updates and done!

Update 1: Expand the data structure

My data structure for the keypad:

[
  [0,  0,  1,  0,  0],
  [0,  2,  3,  4,  0],
  [5,  6,  7,  8,  9],
  [0, 'A','B','C', 0],
  [0,  0, 'D', 0,  0]
]
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Update 2: Adjust the starting location

5 is at [2,0] now

Update 3: Add a clause to the array-cell-checking condition - checking for a value of 0

The iteration portion of my algorithm in JavaScript:

input.reduce(
  (code, line) => {
    key = line.reduce(
      (coords, path) => 
        keypad[coords[0] + map[path][0]] &&
        keypad[coords[0] + map[path][0]][coords[1] + map[path][1]] &&
        keypad[coords[0] + map[path][0]][coords[1] + map[path][1]] !== 0
        ? [ coords[0] + map[path][0],
            coords[1] + map[path][1] ]
        : coords,
        key.slice()
    )
    return code += keypad[key[0]][key[1]]
  }, ""
)
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Part 2: solved!

I did it!!

  • I solved both parts!
  • Using nested reduce()s again!
  • And using my tried and true array traversing techniques!

Bring on Day 1...and hopefully a strong end to an overall fun and relatively fast-solved year!

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