Graph class

Graph.lua

Graph = {}
Graph.__index = Graph

function Graph.new()
    return setmetatable({adjacency_list = {}}, Graph)
end

function Graph:__tostring()
    local str = ""
    for node, list in pairs(self.adjacency_list) do
        str = str .. node .. " ->   "
        for _, adj in ipairs(list) do
            str = str .. adj .. ", "
        end
        str = string.sub(str, 0, -3)
        str = str .. "\n"
    end
    return str
end

function Graph:getNode(node)
    assert(self.adjacency_list[node], "Node '" .. node .. "' does not exist.")
    return self.adjacency_list[node]
end

function Graph:addNode(node)
    assert(not self.adjacency_list[node], "Node '" .. node .. "' already exists") 
    self.adjacency_list[node] = {}
end

function Graph:removeNode(node)
    assert(self.adjacency_list[node], "Node '" .. node .. "' does not exist.")
    for _node, list in pairs(self.adjacency_list) do
        self:removeEdge(node, _node)
    end
    self.adjacency_list[node] = nil
end

function Graph:getEdge(node1, node2)
    assert(self.adjacency_list[node1] and self.adjacency_list[node2],
          "Nodes '" .. node1 .. "' or '" .. node2 .. "' do not exist.")
    for _, node in ipairs(self.adjacency_list[node1]) do
        if node == node2 then return true end
    end
    return false
end

function Graph:addEdge(node1, node2)
    assert(self.adjacency_list[node1] and self.adjacency_list[node2],
          "Nodes '" .. node1 .. "' or '" .. node2 .. "' do not exist.")
    table.insert(self.adjacency_list[node1], node2)
    table.insert(self.adjacency_list[node2], node1)
end

function Graph:removeEdge(node1, node2)
    assert(self.adjacency_list[node1] and self.adjacency_list[node2],
          "Nodes '" .. node1 .. "' or '" .. node2 .. "' do not exist.")
    for i, node in ipairs(self.adjacency_list[node1]) do
        if node == node2 then 
            table.remove(self.adjacency_list[node1], i) 
            break
        end
    end
    for i, node in ipairs(self.adjacency_list[node2]) do
        if node == node1 then
            table.remove(self.adjacency_list[node2], i) 
            break
        end
    end
end

setmetatable(Graph, {__call = function() return Graph.new() end})