hashset implementation

Author: chen0040

README.md

@@ -117,6 +117,24 @@ print(s:delMax()) -- return 10
 print(s:isEmpty()) -- return true
 ```
 
+### HashSet
+
+```lua
+local hashset = require('lualgorithms.data.hashset')
+local hash_func = function(x) return x % 1000 end
+local s = hashset.create(hash_func)
+s:add(100, 2)
+s:add(200, 4)
+s:add(450, 2)
+
+print(s:contains(99)) -- return false
+print(s:contains(100)) -- return true
+print(s:size()) -- return 3
+print(s:isEmpty()) -- return false
+s:remove(100)
+print(s:contains(100)) -- return false)
+```
+
 ### HashMap
 
 ```lua

rockspecs/lualgorithms-1.0-5.rockspec

@@ -26,6 +26,7 @@ build = {
       ["lualgorithms.data.minpq"] = "src/data/minpq.lua",
       ["lualgorithms.data.maxpq"] = "src/data/maxpq.lua",
       ["lualgorithms.data.hashmap"] = "src/data/hashmap.lua",
+      ["lualgorithms.data.hashset"] = "src/data/hashset.lua",
       ["lualgorithms.data.redblacktree"] = "src/data/redblacktree.lua",
       ["lualgorithms.sorting.selection"] = "src/sorting/selection.lua",
       ["lualgorithms.sorting.insertion"] = "src/sorting/insertion.lua",

spec/hashset_spec.lua

@@ -0,0 +1,32 @@
+--
+-- Created by IntelliJ IDEA.
+-- User: chen0
+-- Date: 26/6/2017
+-- Time: 12:03 PM
+-- To change this template use File | Settings | File Templates.
+--
+
+describe('hashset', function()
+    describe('hashset()', function()
+        it('should put and get and remove correctly', function()
+            local hashset = require('data.hashset')
+            local hash_func = function(x) return x % 1000 end
+            local s = hashset.create(hash_func)
+            s:add(100, 2)
+            s:add(200, 4)
+            s:add(450, 2)
+
+            assert.equal(s:contains(99), false)
+            assert.equal(s:contains(100), true)
+            assert.equal(s:size(), 3)
+            assert.equal(s:isEmpty(), false)
+            s:remove(100)
+            assert.equal(s:contains(100), false)
+            assert.equal(s:size(), 2)
+            s:remove(200)
+            s:remove(450)
+            assert.equal(s:isEmpty(), true)
+        end)
+    end)
+end)
+

src/data/hashset.lua

@@ -0,0 +1,103 @@
+--
+-- Created by IntelliJ IDEA.
+-- User: chen0
+-- Date: 28/6/2017
+-- Time: 1:17 PM
+-- To change this template use File | Settings | File Templates.
+--
+
+local hashset = {}
+
+hashset.__index = hashset
+
+hashset.Node = {}
+hashset.Node.__index = hashset.Node
+
+function hashset.Node.create(key)
+    local s = {}
+    setmetatable(s, hashset.Node)
+
+    s.key = key
+    s.next = nil
+
+    return s
+end
+
+function hashset.create(hash)
+    local s = {}
+    setmetatable(s, hashset)
+
+    if hash == nil then
+        hash = function(x) return x end
+    end
+
+    s.s = {}
+    s.N = 0
+    s.hash = hash
+
+    return s
+end
+
+function hashset:add(key)
+    local h = self.hash(key)
+    local x = self.s[h]
+    local found = false
+    while x ~= nil do
+        if x.key == key then
+            found = true
+            break
+        end
+        x = x.next
+    end
+
+    if found == false then
+        local old = self.s[h]
+        self.s[h] = hashset.Node.create(key)
+        self.s[h].next = old
+        self.N = self.N + 1
+    end
+
+end
+
+function hashset:contains(key)
+    local h = self.hash(key)
+    local x = self.s[h]
+    while x ~= nil do
+        if x.key == key then
+            return true
+        end
+        x = x.next
+    end
+    return false
+end
+
+function hashset:size()
+    return self.N
+end
+
+function hashset:isEmpty()
+    return self.N == 0
+end
+
+function hashset:remove(key)
+    local h = self.hash(key)
+    local x = self.s[h]
+    local prev_x = nil
+    while x ~= nil do
+        if x.key == key then
+            if prev_x == nil then
+                self.s[h] = x.next
+            else
+                prev_x.next = x.next
+            end
+            self.N = self.N - 1
+        end
+        prev_x = x
+        x = x.next
+    end
+
+    return nil
+end
+
+return hashset
+