reorg and add code for second edition

10_greedy_algorithms/lua/01_set_covering.lua

@@ -0,0 +1,31 @@
+-- Custom set module
+require "set"
+
+-- You pass an array in, and it gets converted to a set.
+local states_needed = set.new({"mt", "wa", "or", "id", "nv", "ut", "ca", "az"})
+
+local stations = {}
+stations["kone"] = set.new({"id", "nv", "ut"})
+stations["ktwo"] = set.new({"wa", "id", "mt"})
+stations["kthree"] = set.new({"or", "nv", "ca"})
+stations["kfour"] = set.new({"nv", "ut"})
+stations["kfive"] = set.new({"ca", "az"})
+
+local final_stations = set.new()
+
+while next(states_needed) ~= nil do
+    local best_station = nil
+    local states_covered = set.new()
+    for station, states in pairs(stations) do
+        local covered = states_needed * states
+        if covered:len() > states_covered:len() then
+            best_station = station
+            states_covered = covered
+        end
+    end
+
+    states_needed = states_needed - states_covered
+    final_stations:add(best_station)
+end
+
+print(final_stations)

10_greedy_algorithms/lua/set.lua

@@ -0,0 +1,79 @@
+set = {}
+local mt = {__index = set}
+
+function set.new(array)
+    local s = {}
+    if array ~= nil then
+        for _, value in pairs(array) do
+            s[value] = true
+        end
+    end
+    return setmetatable(s, mt)
+end
+
+function set:add(value)
+    if value ~= nil then
+        self[value] = true
+    end
+    return self
+end
+
+function set:remove(value)
+    if value ~= nil then
+        self[value] = nil
+    end
+    return self
+end
+
+function set:len()
+    local len = 0
+    for _ in pairs(self) do
+        len = len + 1
+    end
+    return len
+end
+
+function set.union(a, b)
+    local result = set.new()
+    for key in pairs(a) do
+        result[key] = true
+    end
+    for key in pairs(b) do
+        result[key] = true
+    end
+    return result
+end
+
+function set.difference(a, b)
+    local result = set.new()
+    for key in pairs(a) do
+        result[key] = true
+    end
+    for key in pairs(b) do
+        result[key] = nil
+    end
+    return result
+end
+
+function set.intersection(a, b)
+    local result = set.new()
+    for key in pairs(a) do
+        result[key] = b[key]
+    end
+    return result
+end
+
+function set.tostring(s)
+    local array = {}
+    for key in pairs(s) do
+        array[#array + 1] = tostring(key)
+    end
+    return "{" .. table.concat(array, ", ") .. "}"
+end
+
+mt.__add = set.union
+mt.__sub = set.difference
+mt.__mul = set.intersection
+mt.__tostring = set.tostring
+
+return set