Lesson 05 · Parsing an ASCII grid

Parsing an ASCII grid

Typing out SetWall calls to build a test map is tedious. Today you parse a grid straight from an ASCII drawing, where a dot is open and a hash is a wall, so every later test can describe its map as a picture.

The goal

Parse a multi-line ASCII string into a grid, reading '.' as open and '#' as a wall.

Start here - the target

TO DO

Scenario: An ASCII drawing becomes a grid with the right size and walls

Giventhe three-line string '...' , '.#.' , '...' joined by newlines

Whenit is parsed with ParseGrid

Thenthe grid has Width 3 and Height 3

AndWall(1, 1) is true and every other cell reports Wall false

Background

Building a test map cell by cell does not scale past a few walls. Every pathfinding example in books and articles is drawn as a picture, so we teach the grid to read that picture directly. The convention is the standard one: a dot (.) is an open cell and a hash (#) is a wall. Rows are separated by newlines.

The parse is mechanical: the number of lines is the height, the length of a line is the width, and any # marks a wall at that column and row. Trimming a trailing newline first keeps a final blank line from inventing an empty row. From now on a test can hand you a whole maze as a few lines of text, which is exactly how the spec for every search in this project will describe its map.

Make it work

// split on newlines; height is line count, width is line length
func ParseGrid(s string) *Grid {
  lines := strings.Split(strings.TrimRight(s, "\n"), "\n")
  g := NewGrid(len(lines[0]), len(lines))
  for y, line := range lines {
    for x := 0; x < len(line); x++ {
      if line[x] == '#' { g.SetWall(Coord{x, y}) }
    }
  }
  return g
}

CheckpointDONE

You can build a grid from an ASCII map. Commit and stop here.