reorg and add code for second edition

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