Data Structures Interview Preparation Guide

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malloc: allocate n bytes
calloc: allocate m times n bytes initialized to 0

1. RDBMS Array (i.e. Array of structures)
2. Network data model Graph
3. Hierarchical data model Trees.

Definitions of member functions for the Linked List class are contained in the LinkedList.cpp file.

A linked list application can be organized into a header file, source file and main application file. The first file is the header file that contains the definition of the NODE structure and the LinkedList class definition. The second file is a source code file containing the implementation of member functions of the LinkedList class. The last file is the application file that contains code that creates and uses the LinkedList class.

The appendNode() member function places a new node at the end of the linked list. The appendNode() requires an integer representing the current data of the node.

Linked List is one of the fundamental data structures. It consists of a sequence of nodes, each containing arbitrary data fields and one or two (”links”) pointing to the next and/or previous nodes. A linked list is a self-referential datatype because it contains a pointer or link to another data of the same type. Linked lists permit insertion and removal of nodes at any point in the list in constant time, but do not allow random access.

Each entry in a linked list is called a node. Think of a node as an entry that has three sub entries. One sub entry contains the data, which may be one attribute or many attributes. Another points to the previous node, and the last points to the next node. When you enter a new item on a linked list, you allocate the new node and then set the pointers to previous and next nodes.

The front of the queue is calculated by front = (front+1) % size.

The isEmpty() member method is called within the dequeue process to determine if there is an item in the queue to be removed i.e. isEmpty() is called to decide whether the queue has at least one element. This method is called by the dequeue() method before returning the front element.

Enqueue is the process that places data at the back of the queue in data structure.

Data stored in a queue is actually stored in an array. Two indexes, front and end will be used to identify the start and end of the queue.

When an element is removed front will be incremented by 1. In case it reaches past the last index available it will be reset to 0. Then it will be checked with end. If it is greater than end queue is empty.

When an element is added end will be incremented by 1. In case it reaches past the last index available it will be reset to 0. After incrementing it will be checked with front. If they are equal queue is full.

A Queue is a sequential organization of data in data structure. A queue is a first in first out type of data structure. An element is inserted at the last position and an element is always taken out from the first position.

isEmpty() checks if the stack has at least one element. This method is called by Pop() before retrieving and returning the top element.

The pop() member method removes the value from the top of a stack, which is then returned by the pop() member method to the statement that calls the pop() member method.

push() method, Push is the direction that data is being added to the stack. push() member method places a value onto the top of a stack.

Allocating memory at runtime is called a dynamically allocating memory. In this, you dynamically allocate memory by using the new operator when declaring the array, for example : int grades[] = new int[10];

We can assign a memory address to an element of a pointer array by using the address operator, which is the ampersand (&), in an assignment statement such as ptemployee[0] = &projects[2];

A multidimensional array can be useful to organize subgroups of data within an array. In addition to organizing data stored in elements of an array, a multidimensional array can store memory addresses of data in a pointer array and an array of pointers.

Multidimensional arrays are used to store information in a matrix form.
e.g. a railway timetable, schedule cannot be stored as a single dimensional array.
One can use a 3-D array for storing height, width and length of each room on each floor of a building.

The symbol “*” tells the computer that you are declaring a pointer.
Actually it depends on context.
In a statement like int *ptr; the ‘*’ tells that you are declaring a pointer.
In a statement like int i = *ptr; it tells that you want to assign value pointed to by ptr to variable i.

Yes, a pointer is a variable and can be used as an element of a structure and as an attribute of a class in some programming languages such as C++, but not Java. However, the contents of a pointer is a memory address of another location of memory, which is usually the memory address of another variable, element of a structure, or attribute of a class.

There are two main parts, variable identifier and data type and the third type is optional which is type qualifier like signed/unsigned.

Memory is reserved using data type in the variable declaration. A programming language implementation has predefined sizes for its data types.

For example, in C# the declaration int i; will reserve 32 bits for variable i.

A pointer declaration reserves memory for the address or the pointer variable, but not for the data that it will point to. The memory for the data pointed by a pointer has to be allocated at runtime.

The memory reserved by the compiler for simple variables and for storing pointer address is allocated on the stack, while the memory allocated for pointer referenced data at runtime is allocated on the heap.

Sign of the number is the first bit of the storage allocated for that number. So you get one bit less for storing the number. For example if you are storing an 8-bit number, without sign, the range is 0-255. If you decide to store sign you get 7 bits for the number plus one bit for the sign. So the range is -128 to +127.

Precision refers the accuracy of the decimal portion of a value. Precision is the number of digits allowed after the decimal point.

NULL can be value for pointer type variables.
VOID is a type identifier which has not size.
NULL and void are not same. Example: void* ptr = NULL;