Stacks, Data Structure & Algorithms

Q. Explain what are the stacks? How can we use the stacks  to check whether an expression is correctly parentheses or not. For example (()) is well formed but (() or )()( is not well formed.

 

Ans:

The stack is a data structure that organizes data in a similar way one organizes a pile of coins. The new coin is all the time placed on the top and the oldest is on the bottom of the stack. When we are accessing coins, the last coin on the pile is the first coin which was removed from the stack. If we want to reach the third coin, we should remove the first two coins from the top of the stack first so that the third coin comes on the top of the stack and we can easily remove it. There is no way at all to remove a coin from anywhere other than the top of the stack.

A stack is useful whenever we need to store data and retrieve data in last in, first out order. Let us take an example the computer processes instructions using a stack in which the next instruction to execute is at the top of the stack.

To determine whether an expression is well parentheses or not:- the two conditions should be fulfilled while pushing an expression into a stack. At first, whenever an opening bracket is pushed inside a stack, there should be an occurrence a closing bracket before we reach the last symbol. Whenever a closing bracket is encountered, the top of the stack is popped until the opening bracket is popped out and discarded. If no such type of opening bracket is found and stack is made empty, then this means that the expression is not well parentheses designed.

An algorithm to check that whether an expression is correctly parenthized or not is written below:

flag=TRUE;

clear the stack;

Read a symbol from input string;

while not end of input string and flag do

{

if(symbol= '( ' or symbol= '[' or symbol = '{' )

push(symbol,stack);

else  if(symbol= ') ' or symbol= '[' or symbol =

'{' )

if stack is empty flag=false;

printf("More right parenthesis than left

parenthises");

else c=pop(stack);

match c and the input symbol; If not matched

{     flag=false;

printf("Mismatched

parenthesis");

}

Read the next input symbol;

}

if stack is empty then

printf("parentheses are balanced properly");

else

printf(" More number of left parentheses than right parentheses");

 

Posted Date: 7/10/2012 7:02:20 AM | Location : United States







Related Discussions:- Stacks, Assignment Help, Ask Question on Stacks, Get Answer, Expert's Help, Stacks Discussions

Write discussion on Stacks
Your posts are moderated
Related Questions
Handout 15 COMP 264: Introduction to Computer Systems (Section 001) Spring 2013 R. I. Greenberg Computer Science Department Loyola University Water TowerCampus, Lewis Towers 524 82

The insertion procedure in a red-black tree is similar to a binary search tree i.e., the insertion proceeds in a similar manner but after insertion of nodes x into the tree T, we c

explain quick sort algorithm

design algorithm and flow chart that computes the absolute difference of two values x and y

A graph with n vertices will absolutely have a parallel edge or self loop if the total number of edges is greater than n-1

differentiate between indexing and hashing in file organization

System defined data types:- These are data types that have been defined by the compiler of any program. The C language contains 4 basic data types:- Int, float,  char and doubl

GIVE TRACE OF BINARY SEARCH ALGORITHM BY USING A SUITABLE EXAMPLE.

Explain the concept of hidden lines The problem of hidden lines or surfaces was implicit even in 2-D graphics, but we did not mention it there, because what was intended to be

. Create a decision table that describes the movement of inventory