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Task/Sorting-algorithms-Quicksort/BASIC/sorting-algorithms-quicksort.basic

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+DECLARE SUB quicksort (arr() AS INTEGER, leftN AS INTEGER, rightN AS INTEGER)
+
+DIM q(99) AS INTEGER
+DIM n AS INTEGER
+
+RANDOMIZE TIMER
+
+FOR n = 0 TO 99
+    q(n) = INT(RND * 9999)
+NEXT
+
+OPEN "output.txt" FOR OUTPUT AS 1
+    FOR n = 0 TO 99
+        PRINT #1, q(n),
+    NEXT
+    PRINT #1,
+    quicksort q(), 0, 99
+    FOR n = 0 TO 99
+        PRINT #1, q(n),
+    NEXT
+CLOSE
+
+SUB quicksort (arr() AS INTEGER, leftN AS INTEGER, rightN AS INTEGER)
+    DIM pivot AS INTEGER, leftNIdx AS INTEGER, rightNIdx AS INTEGER
+    leftNIdx = leftN
+    rightNIdx = rightN
+    IF (rightN - leftN) > 0 THEN
+        pivot = (leftN + rightN) / 2
+        WHILE (leftNIdx <= pivot) AND (rightNIdx >= pivot)
+            WHILE (arr(leftNIdx) < arr(pivot)) AND (leftNIdx <= pivot)
+                leftNIdx = leftNIdx + 1
+            WEND
+            WHILE (arr(rightNIdx) > arr(pivot)) AND (rightNIdx >= pivot)
+                rightNIdx = rightNIdx - 1
+            WEND
+            SWAP arr(leftNIdx), arr(rightNIdx)
+            leftNIdx = leftNIdx + 1
+            rightNIdx = rightNIdx - 1
+            IF (leftNIdx - 1) = pivot THEN
+                rightNIdx = rightNIdx + 1
+                pivot = rightNIdx
+            ELSEIF (rightNIdx + 1) = pivot THEN
+                leftNIdx = leftNIdx - 1
+                pivot = leftNIdx
+            END IF
+        WEND
+        quicksort arr(), leftN, pivot - 1
+        quicksort arr(), pivot + 1, rightN
+    END IF
+END SUB