Conversion from Infix to Postfix

This article is part of article series - "Datastructures"

Converting a Fully Parenthesized Infix expression into Postfix expression  

Analysis:

Five types of input characters

• Opening parentheses
• Operands
• Operators
• Closing parentheses
• New line character (\n)

Pseudocode:

********************************************************  
 Function  : main  
  
 Calls     : createStack  
             freeStack                
             pushIntoStack   
             popFromStack   
  
 Called by : NONE   
  
 Input   
 Parameters: Accepts input expression for processing  
    
 Returns   : Converts Fully paranthesized INFIX 
             expression into POSTFIX expression
******************************************************** 

SET i to 0
GET infix expression from user into input_array
SET var with input_array[i]

CALL createStack

WHILE var != end of string

  IF var equals to '(' THEN
  
    CALL pushIntoStack (stack, var)  

  ELSE IF var is a number THEN        
  
    PRINT var  

  ELSE IF var is an arithmetic operator THEN
  
    CALL pushIntoStack (stack, var) 
    
  ELSE IF var equals to ')' THEN

    WHILE stackTop != '('

      IF stackTop is an arithmetic operator THEN

        PRINT stackTop
        popFromStack (stack)

      ENDIF
    
    ENDWHILE

    popFromStack (stack)

  ENDIF

  SET var with input_expression[INCREMENT i]

ENDWHILE

CALL freeStack (stack)

Deleting a Node from a Singly Linked List

This article is part of article series - "Datastructures"

Previous Article: Implementation of Singly Linked List.
Next Article: Reversing a Singly Linked List

Deletion of a Node from a Singly Linked List
Similar to insertion we have three cases for deleting a Node from a Singly Linked List.

• Deleting First Node in Singly Linked List
  
  To complete deletion of firstNode in the list we have to change Head pointing to Next of firstNode.
  
  Pseudocode:

  firstNode = Head
  
  Head = firstNode->Next
  
  free firstNode

  Complexity:
  Time Complexity: O(1)
  Space Complexity: O(1)

Detecting First Node in a Loop in the List

This article is part of article series - "Datastructures"

Previous Article: Detecting a Loop in Singly Linked List - Tortoise and Hare.
Next Article: Finding Nth node from end of a Singly Linked List.

Once we confirm that there is a Loop in a Singly Linked List we will see how to determine first node of the loop.

Finding Nth node from end of a Singly Linked List

This article is part of article series - "Datastructures"

Previous Article: Finding first node in a Loop in Singly Linked List.

Figure 1: Singly Linked List

Solution 01 - Brute Force Approach:

1. Start at First Node of the List (call it curNodePtr).
2. Assign curNodePtr to tmpPtr and count number of nodes after the curNodePtr.
3. If number of nodes after curNodePtr are equal to N nodes or tmpPtr reaches END then break. If tmPtr reaches END but count not equal to N then return since we can't find the Nth node from the end of the Singly Linked List.
4. Move the curNodePtr one step forward in the Linked List i.e curNodePtr now points to its next node in the list and start again from STEP-2.

Reversing a Singly Linked List

This article is part of article series - "Datastructures"

Previous Article: Deleting a Node from a Singly Linked List.
Next Article: Detecting a Loop in Singly Linked List - Tortoise and Hare.

Let us see how to reverse a Singly Linked List.

Figure-1: Singly Linked List

Pseudocode:

cur_ptr = HEAD->NEXT
prev_ptr = NULL

forever:

   if cur_ptr == NULL
   break

   tmp_ptr  = prev_ptr
   prev_ptr = cur_ptr
   cur_ptr  = cur_ptr->NEXT
   
   prev_ptr->NEXT = tmp_ptr

HEAD->NEXT = prev_ptr

Complexity:
Time Complexity: O(n)
Space Complexity: O(3)

If we try on the example in Figure-1 we get the output as shown below

Figure-2: After reversing the Singly Linked List

Previous Article: Deleting a Node from a Singly Linked List.
Next Article: Detecting a Loop in Singly Linked List - Tortoise and Hare.