quick sort implementation

Author: chen0040

README.md

@@ -279,3 +279,25 @@ for i=0,(a:size()-1) do
 end
 ```
 
+### Sorting (Quick Sort)
+
+```lua
+local list = require("lualgorithms.data.list")
+local a = list.create()
+a:add(100)
+a:add(200)
+a:add(300)
+a:add(600)
+a:add(200)
+a:add(400)
+a:add(340)
+a:add(120)
+a:add(10)
+
+local quicksort = require("lualgorithms.sorting.quicksort")
+quicksort.sort(a, function(a1, a2) return a1 - a2 end)
+
+for i=0,(a:size()-1) do
+    print(a:get(i))
+end
+```

rockspecs/lualgorithms-1.0-5.rockspec

@@ -32,5 +32,6 @@ build = {
       ["lualgorithms.sorting.insertion"] = "src/sorting/insertion.lua",
       ["lualgorithms.sorting.shellsort"] = "src/sorting/shellsort.lua",
       ["lualgorithms.sorting.mergesort"] = "src/sorting/mergesort.lua",
+      ["lualgorithms.sorting.quicksort"] = "src/sorting/quicksort.lua",
    }
 }

spec/quick_sort_spec.lua

@@ -0,0 +1,32 @@
+--
+-- Created by IntelliJ IDEA.
+-- User: chen0
+-- Date: 28/6/2017
+-- Time: 9:16 AM
+-- To change this template use File | Settings | File Templates.
+--
+
+describe("Merge Sort", function()
+    it("should sort ascendingly", function()
+        local list = require("data.list")
+        local a = list.create()
+        a:add(100)
+        a:add(200)
+        a:add(300)
+        a:add(600)
+        a:add(200)
+        a:add(400)
+        a:add(340)
+        a:add(120)
+        a:add(10)
+
+        local quicksort = require("sorting.quicksort")
+        quicksort.sort(a, function(a1, a2) return a1 - a2 end)
+
+        for i=0,(a:size()-2) do
+            assert.is_true(a:get(i) <= a:get(i+1))
+        end
+
+    end)
+end)
+

src/sorting/quicksort.lua

@@ -0,0 +1,62 @@
+--
+-- Created by IntelliJ IDEA.
+-- User: chen0
+-- Date: 29/6/2017
+-- Time: 10:04 AM
+-- To change this template use File | Settings | File Templates.
+--
+
+local quicksort = {}
+quicksort.__index = quicksort
+
+function quicksort.sort(a, comparator)
+    quicksort._sort(a, 0, a:size()-1, comparator)
+end
+
+function quicksort._sort(a, lo, hi, comparator)
+    if lo >= hi then
+        return
+    end
+
+    local j = quicksort._partition(a, lo, hi, comparator)
+    quicksort._sort(a, lo, j-1, comparator)
+    quicksort._sort(a, j+1, hi, comparator)
+end
+
+function quicksort._partition(a, lo, hi, comparator)
+    local i = lo
+    local j = hi + 1
+    local v = a:get(lo)
+    while true do
+        i = i + 1
+        while comparator(a:get(i), v) < 0 do
+            i = i+1
+            if i >= hi then
+                break
+            end
+        end
+        j = j - 1
+        while comparator(v, a:get(j)) < 0 do
+            j = j - 1
+            if j <= lo then
+                break
+            end
+        end
+
+        if i >= j then
+            break
+        end
+
+        quicksort.exchange(a, i, j)
+    end
+    quicksort.exchange(a, lo, j)
+    return j
+end
+
+function quicksort.exchange(a, i, j)
+    local temp = a:get(i)
+    a:set(i, a:get(j))
+    a:set(j, temp)
+end
+
+return quicksort