Stack and its application, Study notes of Data Structures and Algorithms

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Data Structures and Algorithms

LECTURE 08 – STACK APPLICATIONS

Applications of Stack

• Stack is one of the most important data structures in computer science
  • Compilers use stacks to evaluate expressions
  • Stacks are great for reversing things, matching up related pairs of things, etc.
  • Stack programming problems:
    • Examine an algebraic expression to see if its braces { } and other operators match
    • Convert infix expressions to postfix or prefix
    • Reverse letters in a string, reverse words in a line, or reverse a list of numbers

Why do we need Infix to Pre/Postfix Conversion?

• Infix notations are easily understood by Humans; however, the operator precedence has

to be resolved, i.e., 2-35+6 = 2-(35)+

• The precedence of rules are easily understood by humans, what about machines?
• The biggest of advantage of Pre/Postfix notations is that the governing rules are

satisfied while parsing the expression

Infix to Postfix

Infix to Postfix using Stack else { while (c has a precedence lower than or equal to the top of the stack) Output += Pop(S) Push(c, S) } } if (c == ')') { while (Pop(S) != '(') Output += Pop(S) } } while (!isEmpty(S)) Output += Pop(S)

23/(2-1)+53 to 2321-/53+

• 3(4+5)/2 to 345+2/ =