95 lines
2.4 KiB
Lua
95 lines
2.4 KiB
Lua
describe("dijkstras algorithm with binaryheap", function()
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-- See https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
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it("calculates knight's shortest path", function()
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-- See http://stackoverflow.com/questions/2339101
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local binaryheap = require 'binaryheap'
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local ROWS = 8
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local COLS = 8
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local unvisited = binaryheap.minUnique()
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local function Cell(x, y)
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return x .. '_' .. y
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end
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local function Coordinates(cell)
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local x, y = cell:match('(%d+)_(%d+)')
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return x, y
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end
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local function neighbours(cell)
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local x, y = Coordinates(cell)
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local gen = coroutine.wrap(function()
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coroutine.yield(x - 1, y - 2)
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coroutine.yield(x - 1, y + 2)
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coroutine.yield(x + 1, y - 2)
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coroutine.yield(x + 1, y + 2)
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coroutine.yield(x - 2, y - 1)
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coroutine.yield(x - 2, y + 1)
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coroutine.yield(x + 2, y - 1)
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coroutine.yield(x + 2, y + 1)
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end)
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return coroutine.wrap(function()
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for xx, yy in gen do
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if 1 <= xx and xx <= COLS and
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1 <= yy and yy <= ROWS then
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coroutine.yield(Cell(xx, yy))
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end
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end
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end)
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end
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for y = 1, ROWS do
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for x = 1, COLS do
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local cell = Cell(x, y)
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unvisited:insert(math.huge, cell)
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end
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end
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unvisited:update('1_1', 0)
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local final_distance = {}
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while unvisited:peekValue() do
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local current, current_distance = unvisited:peek()
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assert(not final_distance[current])
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final_distance[current] = current_distance
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unvisited:remove(current)
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-- update neighbours
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local new_distance = current_distance + 1
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for neighbour in neighbours(current) do
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if unvisited.reverse[neighbour] then
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local pos = unvisited.reverse[neighbour]
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local distance = unvisited.values[pos]
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if distance > new_distance then
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unvisited:update(neighbour, new_distance)
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end
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end
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end
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end
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local rows = {}
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for y = 1, ROWS do
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local row = {}
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for x = 1, COLS do
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local cell = Cell(x, y)
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local distance = final_distance[cell]
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table.insert(row, distance)
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end
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table.insert(rows, table.concat(row, ' '))
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end
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assert.equal([[
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0 3 2 3 2 3 4 5
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3 4 1 2 3 4 3 4
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2 1 4 3 2 3 4 5
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3 2 3 2 3 4 3 4
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2 3 2 3 4 3 4 5
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3 4 3 4 3 4 5 4
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4 3 4 3 4 5 4 5
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5 4 5 4 5 4 5 6]],
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table.concat(rows, '\n'))
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end)
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end)
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