Knight Tour problem in Lua

knights.lua

#!/usr/bin/env lua

--
-- Copyright (c) 2023 Gabriel G. de Brito
--
-- Permission is hereby granted, free of charge, to any person obtaining a copy
-- of this software and associated documentation files (the "Software"), to deal
-- in the Software without restriction, including without limitation the rights
-- to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-- copies of the Software, and to permit persons to whom the Software is
-- furnished to do so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in
-- all copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-- SOFTWARE.
--

create_line = function(n)
    local l = {}
    for i = 1, n do
        table.insert(l, 0)
    end

    return l
end

create_grid = function(n)
    local g = {}
    for i = 1, n do
        table.insert(g, create_line(n))
    end

    return g
end

print_grid = function(grid, n)
    for i = 1, n do
        for j = 1, n do
            if grid[i][j] == 0 then
                io.write("|   ")
            else
                io.write("|" .. string.format("%03d", grid[i][j]))
            end
        end
        io.write("|\n")
    end
end

clrscr = function()
    io.write "\27[2J"
    io.write "\27[H"
end

hidecursor = function()
    io.write "\27[?25l"
end

showcursor = function()
    io.write "\27[?25h"
end

getmov = function(x, y, n)
    local mov = {}
    local st = {
        { x = -2, y = 1 },
        { x = -2, y = -1 },
        { x = -1, y = 2 },
        { x = -1, y = -2 },
        { x = 1, y = 2 },
        { x = 2, y = 1 },
        { x = 1, y = -2 },
        { x = 2, y = -1 },
    }

    for i = 1, 8 do
        local s = { x = x + st[i].x, y = y + st[i].y }
        if s.x > 0 and s.x <= n and s.y > 0 and s.y <= n then
            table.insert(mov, s)
        end
    end

    return mov
end

knight_tour = function(grid, n, x, y, h)
    grid[x][y] = h
    clrscr()
    -- print_grid(grid, n)
    -- os.execute("sleep 0.0003")

    if h == n * n then
        return true
    end

    local pos = getmov(x, y, n)
    for i, m in ipairs(pos) do
        if grid[m.x][m.y] == 0 then
            if knight_tour(grid, n, m.x, m.y, h + 1) then
                return true
            end
        end
    end

    grid[x][y] = 0
    return false
end

clrscr()
hidecursor()

size = 5

grid = create_grid(size)
if knight_tour(grid, size, size, size, 1) then
    print_grid(grid, size)
    print "solution found!!"
else
    print_grid(grid, size)
    print "no solution found"
end

showcursor()