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{"0":"Algorithms","1":"Selection","2":"Iteration","3":"Arrays","4":"Records","5":"ENUMs","6":"Custom Modules","7":"Files","8":"Object-Oriented Programming","9":"Abstract Data Types","10":"Sets","11":"Pointers","12":"Recursion","13":"Exam Questions","14":"Games","15":"Mathematics","16":"Art","17":"Utilities","18":"Other"}
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b <-- 1
a <-- 2
b <-- 3
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a
b
1
2
3
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{"c":"\/\/ * Code Author: MC_PHILLIPS\n\/\/ * Date: 2025\/10\/03\n\/\/ * Description: Demo showing linked lists using arrays and pointers. Lots of global variables but that is how the questions are in the exam.\n\/\/ * Categories: \n\n\/\/\"\"\"PSEUDO CODE FOR LINKED LIST\r\n\/\/EXERCISES AT END OF PAGE\r\n\r\n\/\/this module uses global variables , that are used in some of the procedures.\r\n\/\/Yes I know its not best practice but it makes things easier.\r\n\/\/they are declared and initialized after the function definitions.\r\n\/\/they are:\r\n\/\/FreePtr : INTEGER\r\n\/\/HeadPtr : INTEGER\r\n\/\/TailPtr : INTEGER\r\n\/\/CurrentPtr : INTEGER\r\n\/\/Null : INTEGER [Null <- 0, we are using 1 as the start \/\/index of arrays]\r\n\/\/aData : ARRAY[1:5] OF Node\r\n\/\/\"\"\"\r\nTYPE Node\r\n DECLARE Data : INTEGER\r\n DECLARE NextItem : INTEGER\r\nENDTYPE\r\n\r\n\r\nFUNCTION GetValue(Index : INTEGER) RETURNS INTEGER\r\n DECLARE Value : INTEGER\r\n Value <- aData[Index].Data\r\n RETURN Value\r\nENDFUNCTION\r\n\r\n\r\nPROCEDURE QuitIt()\r\n \/\/to stop execution -bug in the pseudococde interpreter\r\n DECLARE X:STRING\r\n X <- \"1\"\r\n OUTPUT RIGHT(X,1)\r\n \r\nENDPROCEDURE\r\n\r\n\r\nPROCEDURE DEBUGOUT()\r\n OUTPUT \"HeadPtr:\",HeadPtr\r\n OUTPUT \"TailPtr:\",TailPtr\r\n OUTPUT \"FreePtr:\",FreePtr\r\n OUTPUT \"Nodes:\"\r\n DECLARE i : INTEGER\r\n DECLARE s : STRING\r\n FOR i <- 1 TO ListLength\r\n s \u2190 \" \"\r\n IF i = HeadPtr THEN\r\n s \u2190 s & \"Head\"\r\n ENDIF \r\n IF i = TailPtr THEN\r\n s \u2190 s & \" Tail\" \r\n ENDIF \r\n IF i = FreePtr THEN\r\n s \u2190 s & \"Free\"\r\n ENDIF \r\n s \u2190 RIGHT(s & \"->\",12)\r\n OUTPUT s,i,\":\",aData[i].Data,\" ->\",aData[i].NextItem\r\n NEXT i\r\nENDPROCEDURE\r\n\r\n\r\nPROCEDURE TraverseListInOrder()\r\n DECLARE Ptr : INTEGER\r\n Ptr <- HeadPtr\r\n WHILE Ptr <> Null\r\n OUTPUT aData[Ptr].Data,\":\",Ptr\r\n Ptr <- aData[Ptr].NextItem\r\n ENDWHILE\r\nENDPROCEDURE\r\n\r\n\r\nFUNCTION PUSH(Value : INTEGER) RETURNS INTEGER\r\n\/\/ this inserts an item into a linked list so the list is naturally sorted ASC (lowest to highest)\r\n IF FreePtr = Null THEN\r\n \/\/no space in array\r\n RETURN Null\r\n ENDIF\r\n DECLARE PreviousPtr : INTEGER\r\n DECLARE InsertedPtr : INTEGER\r\n DECLARE FOUND : BOOLEAN\r\n \/\/if starting a list\r\n IF HeadPtr = Null THEN \r\n \/\/FreePtr moves to used list. Get the new FreePtr\r\n InsertedPtr <- FreePtr\r\n FreePtr <- aData[FreePtr].NextItem\r\n aData[InsertedPtr].Data <- Value\r\n aData[InsertedPtr].NextItem <- Null\r\n \/\/reset pointers\r\n HeadPtr <- InsertedPtr\r\n TailPtr <- InsertedPtr \/\/\r\n RETURN HeadPtr \/\/ should be 1.\r\n ELSE\r\n CurrentPtr <- HeadPtr\r\n FOUND <- FALSE\r\n PreviousPtr <- Null\r\n WHILE CurrentPtr > Null AND FOUND = FALSE\r\n OUTPUT \"In While Loop\"\r\n OUTPUT \"CurrentPtr\",CurrentPtr,\"FOUND:\",FOUND\r\n OUTPUT \"GetValue:\",CurrentPtr,GetValue(CurrentPtr)\r\n IF Value < GetValue(CurrentPtr) THEN\r\n OUTPUT \"INSERTING BEFORE:\", CurrentPtr\r\n \/\/insert the value into free list, adjust the pointers\r\n \/\/if PreviousPtr is null then we're at the start of the list\r\n InsertedPtr <- FreePtr\r\n FreePtr <- aData[FreePtr].NextItem\r\n IF PreviousPtr <> Null THEN\r\n OUTPUT \"Pointing Previous item to new item\"\r\n aData[PreviousPtr].NextItem <- InsertedPtr\r\n ELSE\r\n OUTPUT \"Changing Head pointer\"\r\n HeadPtr <- InsertedPtr\r\n ENDIF\r\n OUTPUT \"Setting Values\"\r\n aData[InsertedPtr].Data <- Value\r\n aData[InsertedPtr].NextItem <- CurrentPtr\r\n FOUND <- TRUE\r\n \/\/return position of insert\r\n \/\/RETURN InsertedPtr\r\n ELSE\r\n PreviousPtr <- CurrentPtr\r\n CurrentPtr <- aData[CurrentPtr].NextItem\r\n ENDIF\r\n OUTPUT \"End of while loop\"\r\n \/\/QuitIt()\r\n ENDWHILE\r\n ENDIF\r\n IF FOUND = TRUE THEN\r\n OUTPUT \"Returning inserted pointer\", InsertedPtr \r\n RETURN InsertedPtr\r\n ENDIF\r\n \/\/add to end of list. FOUND should be FALSE here.\r\n \/\/TailPtr shouldequal PreviousPtr\r\n OUTPUT \"Found = False\",\" CurrentPtr:\",CurrentPtr,\" PreviousPtr:\",PreviousPtr\r\n IF FOUND = FALSE THEN\r\n InsertedPtr <- FreePtr\r\n FreePtr <- aData[FreePtr].NextItem\r\n aData[InsertedPtr].Data <- Value\r\n aData[InsertedPtr].NextItem <- Null \/\/ new tail\r\n aData[TailPtr].NextItem <- InsertedPtr \/\/change current tail\r\n TailPtr <- InsertedPtr\r\n \r\n RETURN InsertedPtr \/\/ or TailPtr\r\n ENDIF\r\nENDFUNCTION\r\n \r\nFUNCTION POP(Value : INTEGER) RETURNS INTEGER\r\n \/\/ MORE LIKE DELETE. Searches for Value then deletes item.\r\n \/\/Returns position item was found - just for testing unnecessary really.\r\n IF HeadPtr = Null THEN\r\n RETURN Null\r\n ENDIF\r\n DECLARE PreviousPtr : INTEGER\r\n PreviousPtr <- Null\r\n CurrentPtr <- HeadPtr\r\n WHILE CurrentPtr <> Null DO\r\n IF aData[CurrentPtr].Data = Value THEN\r\n DECLARE NextItemPointer : INTEGER\r\n NextItemPointer <- aData[CurrentPtr].NextItem\r\n IF CurrentPtr = HeadPtr THEN\r\n \/\/no previous ptr\r\n HeadPtr <- aData[HeadPtr].NextItem\r\n ELSE\r\n aData[PreviousPtr].NextItem <- NextItemPointer\r\n ENDIF\r\n IF NextItemPointer = Null THEN\r\n \/\/end of list\r\n TailPtr <- PreviousPtr\r\n ENDIF\r\n \/\/make deleted item first item in freelist, make it point to current FreePointer\r\n \/\/if at start of list no previous pointer so check for it\r\n IF CurrentPtr = HeadPtr THEN\r\n HeadPtr <- aData[HeadPtr].NextItem\r\n ENDIF\r\n aData[CurrentPtr].NextItem <- FreePtr\r\n FreePtr <- CurrentPtr\r\n RETURN CurrentPtr\r\n ENDIF\r\n PreviousPtr <- CurrentPtr\r\n CurrentPtr <- aData[CurrentPtr].NextItem\r\n ENDWHILE\r\n\r\n \/\/CurrentPtr should be NULL here - item wasnt in the list\r\n RETURN CurrentPtr\r\nENDFUNCTION\r\n\r\n\r\n\r\n\r\n \r\nOUTPUT \"Starting\"\r\n\/\/Linked List Demo\r\nDECLARE FreePtr : INTEGER\r\nDECLARE HeadPtr : INTEGER\r\nDECLARE TailPtr : INTEGER\r\nDECLARE CurrentPtr : INTEGER\r\nDECLARE Null : INTEGER\r\nNull <- 0\r\n\r\n\r\n\r\n\r\n\/\/set listlength here so its easy to refer to\r\nDECLARE ListLength : INTEGER\r\nListLength <- 5\r\nDECLARE aData : ARRAY[1:5] OF Node\r\n\r\n\r\n\/\/set freelist pointers - initially all items are in the free lsit\r\nDECLARE i : INTEGER\r\nFOR i <- 1 TO ListLength - 1\r\n aData[i].Data <- 0\r\n aData[i].NextItem <- i+1\r\nNEXT i\r\n\/\/last item in free list does not point to another item so set NextItem to -1 (==Null in PSC)\r\naData[ListLength].Data <- 0\r\naData[ListLength].NextItem <- Null\r\nFreePtr <- 1\r\nHeadPtr <- Null\r\nTailPtr <- Null\r\nCurrentPtr <- Null\r\n\r\n\r\nOUTPUT \"Initialised\"\r\nCALL QuitIt()\r\nCALL DEBUGOUT()\r\nBREAKPOINT\r\n\/\/test\r\nDECLARE Index : INTEGER\r\nIndex <-PUSH(2)\r\nCALL DEBUGOUT()\r\nIndex <- PUSH(9)\r\nCALL DEBUGOUT()\r\nIndex <- PUSH(5)\r\nCALL DEBUGOUT()\r\nIndex <- PUSH(8)\r\nCALL DEBUGOUT()\r\nIndex <- PUSH(6)\r\nCALL DEBUGOUT()\r\nOUTPUT \"List In Order\"\r\n\r\n\r\nCALL TraverseListInOrder()\r\nIndex <-POP(9)\r\nOUTPUT \"List In Order after deleting 10\"\r\nCALL DEBUGOUT()\r\nCALL TraverseListInOrder()\r\n\r\n\r\n\r\n\/\/\r\n\/\/Translate the pseudocode into python.","t":"13CPC Linked List Demo"}
