June 2018 Update

Task/Quickselect-algorithm/Julia/quickselect-algorithm.julia

@@ -0,0 +1,2 @@
+v = [9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
+@show v select(v, 1:10)

Task/Quickselect-algorithm/Maple/quickselect-algorithm.maple

@@ -0,0 +1,36 @@
+part := proc(arr, left, right, pivot)
+	local val,safe,i:
+	val := arr[pivot]:
+	arr[pivot], arr[right] := arr[right], arr[pivot]:
+	safe := left:
+	for i from left to right do
+		if arr[i] < val then
+			arr[safe], arr[i] := arr[i], arr[safe]:
+			safe := safe + 1:
+		end if:
+	end do:
+	arr[right], arr[safe] := arr[safe], arr[right]:
+	return safe:
+end proc:
+
+quickselect := proc(arr,k)
+	local pivot,left,right:
+	left,right := 1,numelems(arr):
+	while(true)do
+		if left = right then return arr[left]: end if:
+		pivot := trunc((left+right)/2);
+		pivot := part(arr, left, right, pivot):
+		if k = pivot then
+			return arr[k]:
+		elif k < pivot then
+			right := pivot-1:
+		else
+			left := pivot+1:
+		end if:
+	end do:
+end proc:
+roll := rand(1..20):
+demo := Array([seq(roll(), i=1..20)]);
+map(x->printf("%d ", x), demo):
+print(quickselect(demo,7)):
+print(quickselect(demo,14)):

Task/Quickselect-algorithm/Ring/quickselect-algorithm.ring

@@ -2,19 +2,19 @@ aList = [9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
 see partition(aList, 9, 4, 2) + nl
 
 func partition list, left, right, pivotIndex
-     pivotValue = list[pivotIndex]
-     temp = list[pivotIndex]
-     list[pivotIndex] = list[right]
-     list[right]  = temp
-     storeIndex = left
-     for i = left to right-1
-         if list[i] < pivotValue
-            temp = list[storeIndex]
-            list[storeIndex] = list[i]
-            list[i] = temp
-            storeIndex++ ok
-         temp = list[right]
-         list[right] = list[storeIndex]
-         list[storeIndex] = temp
-     next
-     return storeIndex
+       pivotValue = list[pivotIndex]
+       temp = list[pivotIndex]
+       list[pivotIndex] = list[right]
+       list[right]  = temp
+       storeIndex = left
+       for i = left to right-1
+            if list[i] < pivotValue
+               temp = list[storeIndex]
+               list[storeIndex] = list[i]
+               list[i] = temp
+               storeIndex++ ok
+            temp = list[right]
+            list[right] = list[storeIndex]
+            list[storeIndex] = temp
+       next
+       return storeIndex