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Showing posts from February, 2017

### Infix to Prefix conversion using Stack

This post is about conversion of Infix expression to Prefix conversion. For this conversion we take help of stack data structure, we need to push and pop the operators in and out of the stack.

Infix expressions are the expressions that we normally use,eg. 5+6-7; a+b*c etc. Prefix expressions are the expressions in which the 2 operands are preceded by the operator eg. -+567 , +a*bc etc.

This method is very similar to the method that we used to convert Infix to Postfix but the only difference is that here we need to reverse the input string before conversion and then reverse the final output string before displaying it.

NOTE: This changes one thing that is instead of encountering the opening bracket we now first encounter the closing bracket and we make changes accordingly in our code.

So, to convert an infix expression to a prefix expression we follow the below steps
(we have 2 string, 1st is the input infix expression string 2nd is the output string which is empty initially)

We first revers…

### Infix to Postfix conversion using Stack

This post is about conversion of Infix expression to Postfix conversion. For this conversion we take help of stack data structure, we need to push and pop the operators in and out of the stack.

Infix expressions are the expressions that we normally use,eg. 5+6-7; a+b*c etc. Postfix expressions are the expressions in which the 2 operands are followed by the operator eg. 56+7- , abc*+ etc.

So inorder to convert an infix expression to a postfix expression we follow the below steps
(we have 2 string, 1st is the input infix expression string 2nd is the output string which is empty initially)

We start by going through the characters of the infix expression one by one.If we come across an operand we simply copy it to the Postfix output string.If we come across any opening parenthesis we push it on the stack.If we come across any closing parenthesis we pop the stack till we find the corresponding opening parenthesis.If we come across an operator then we have 2 cases based on the precedence of the…

### 4 Different methods to swap 2 numbers

Swapping 2 numbers is one of the favorite questions asked to a lot of people during their interviews. There are a lot of ways to swap 2 numbers. In this post we have 4 methods that can be used to swap 2 numbers.

First Method : Using addition and subtraction method This method is a simple method that can be used to swap 2 numbers, the method can be used for all integer, float and double variables. The method involves one addition and two subtraction operations.

Second Method : Using multiplication and division operators
This method is simply obtained by replacing + by * and - by / operator in the above method, but this method cannot be used when one of the numbers is 0 as it involves division operation.

Third Method : Using the EX-OR operation
This method involves repeated ex-or operations between 2 numbers to swap 2 numbers. But this method can be used only for integers and cannot be used for float or double variables as bit operations for them are not defined.

Fourth Method : Using temp…

### Shell Sort

Shell sort is a in-place comparison sort method to sort the element. Unlike other sorting methods in this method we start by sorting elements that are far apart or at fixed gap from each other and after every iteration we get partially sorted sublists.

Let us consider an array of 7 elements and sort them by gap of 3.

In the above example we see that as we have an array we compare element that are 3 gaps away so we sort the sublists (a0, a3, a6) , (a1, a4) , (a2, a5) .

The sorting of these sublists can be done using any method for my program I have used Insertion sort.
After every iteration we decrease the gap unitl we reach the gap of one where it simply compares the adjacent elements. Chosing the values of gaps is very important as has effects on the complexity of the sorting.

C ProgramC++ ProgramJava programPython ProgramC Program C++ Program Java Program Python Program Sample input and output to check the program

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### Double Hashing

Hashing is a technique used for storing , searching and removing elements in almost constant time. Hashing is done with help of a hash function that generates index for a given input, then this index can be used to search the elements, store an element, or remove that element from that index.

A hash function is a function that is used to map the data elements to their position in the data structure used. For example if we use an array to store the integer elements then the hash function will generate position for each element so that searching, storing and removing operation on the array can be done in constant time that is independent of the number of elements in the array. For better look at the example below.

now we face a problem if for 2 numbers same position is generated example consider elements 1 and 14

1 % 13 = 1

14 % 13 = 1

so when we get 1 we store it at the first position, but when we get 14 we see that the position 1 is already taken, this is a case of collision.

Inorder…