2016 Update

Task/Quickselect-algorithm/Lua/quickselect-algorithm.lua

@@ -0,0 +1,33 @@
+function partition (list, left, right, pivotIndex)
+    local pivotValue = list[pivotIndex]
+    list[pivotIndex], list[right] = list[right], list[pivotIndex]
+    local storeIndex = left
+    for i = left, right do
+        if list[i] < pivotValue then
+            list[storeIndex], list[i] = list[i], list[storeIndex]
+            storeIndex = storeIndex + 1
+        end
+    end
+    list[right], list[storeIndex] = list[storeIndex], list[right]
+    return storeIndex
+end
+
+function quickSelect (list, left, right, n)
+    local pivotIndex
+    while 1 do
+        if left == right then return list[left] end
+        pivotIndex = math.random(left, right)
+        pivotIndex = partition(list, left, right, pivotIndex)
+        if n == pivotIndex then
+            return list[n]
+        elseif n < pivotIndex then
+            right = pivotIndex - 1
+        else
+            left = pivotIndex + 1
+        end
+    end
+end
+
+math.randomseed(os.time())
+local vec = {9, 8, 7, 6, 5, 0, 1, 2, 3, 4}
+for i = 1, 10 do print(i, quickSelect(vec, 1, #vec, i) .. " ") end