Data Structures Previous Year Questions (page 3)

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Inserting at the beginning of a linked list only changes the head pointer, which is O(1). An array must shift every element, which is O(n). Array access by index is faster.

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fwrite() writes a block of data, and fseek() sets the file position pointer. ftell() only returns the current position; rewind() is the function that moves to the beginning.

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A doubly linked list has both next and prev pointers, so it can be traversed forward and backward. It uses more memory than a singly linked list.

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A message queue stores messages in FIFO order: messages are added at the rear and the receiver takes them from the front.

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Row-major address = Base + (i × columns + j) × size = 5000 + (2 × 5 + 3) × 2 = 5000 + 26 = 5026.

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In C an array is declared as type name[size], so int array[15]; declares 15 integers. The other forms are not valid C syntax.

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The list is A(0) → C(4) → E(1) → B(2). X goes into free location 3. E's pointer changes to 3, and X points to B at 2, giving A → C → E → X → B as in option B.

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*arr is arr[0], so *(*arr + 1) is arr[0][1] = 2, not 4. The other three expressions all mean arr[1][1] = 4.

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Option D is incorrect: a singly linked list has no index arithmetic, so you must walk from the head node by node to reach an element. It has sequential access, not random access.

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CALL pushes the return address onto the stack. The stack grows downward, so SP is decreased by 2 (or by 4 on 32-bit systems) before the address is stored.

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A linked list must be traversed node by node from the head. In the worst case the key is the last node or is missing, which needs n comparisons, so the time is O(n).

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The sender signs a hash (message digest) of the message. The receiver recomputes the hash and compares it; any change to the message gives a different hash, so the hash value guarantees integrity.

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[] binds tighter than *, so int *arr[5] is an array of 5 pointers to int. The parentheses in int (*arr)[5] make arr a single pointer to an array of 5 ints.

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In PHP, a parameter declared with & (function f(&$x)) is a reference to the caller's variable, so changing it inside the function changes the original value. Any type can be passed by reference.

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Bubble sort makes (n-1) + (n-2) + ... + 1 = n(n-1)/2 comparisons in the worst case. For n = 15 that is 15 x 14 / 2 = 105.

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Copying the data needs a single pass through the list, visiting each of the n nodes once, so it takes O(n) operations. The later sorting step is what needs O(n log n).

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After deleting a[0], each of the remaining n - 1 elements must move one position left, so n - 1 shift operations are needed.

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Start at location 0 (A, next 4), then 4 (C, next 1), 1 (E, next 3), 3 (X, next 2), 2 (B, next NULL). So the order is A, C, E, X, B.

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In a declaration, * makes j a pointer variable that can store the address of an int. It does not allocate the pointed-to memory or multiply anything.

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A NULL pointer explicitly marks that the pointer refers to no valid memory, so the code can test if (p == NULL) before use, avoiding accidental use of garbage or dangling addresses.

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In an acyclic-graph directory, a shared file or subdirectory is usually implemented with a link, a special directory entry (symbolic link) that holds the path of the real file, so the same file appears in several directories without copying.

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In char names[N][L], the first dimension is the number of strings (rows) and the second is the maximum length of each string, including the null character.

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ptr is never incremented inside the loop, so *ptr always reads arr[0] = 1, printing 1 five times (after "Array Elements: "). To print 1 2 3 4 5 the loop would need ptr[i] or *(ptr + i).

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Merge sort suits linked lists: it needs only sequential access, splits the list by moving pointers, merges without extra arrays and runs in O(n log n). Other sorts are O(n²) or need random access.

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asort() sorts an array by value in ascending order while keeping each key associated with its value. sort() re-indexes the keys, and ksort() sorts by key.

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An array name is not a modifiable lvalue, so a string cannot be assigned with arr = "..." after declaration (and "consultancy" needs 12 chars, more than 6). Strings must be given at initialisation or copied with strcpy.

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Each node of a singly linked list holds the data and a pointer (address) to the next node; the last node's pointer is NULL. A previous-node pointer is used in doubly linked lists.

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To reach the k-th element in a singly linked list you must traverse from the head, O(n), whereas arrays allow direct access by index. O(1) insertion and deletion at the start and variable size are advantages.

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Removing the first element of a dynamic array requires shifting the remaining n - 1 elements one place left, so it takes O(n) time.

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A DOM parser loads the whole XML document into memory as a tree of objects. SAX is event-based and builds no tree.

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A queue is FIFO (first in, first out), so the first element inserted is the first removed. A stack is LIFO.

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byte is one of Java's eight primitive types (byte, short, int, long, float, double, char, boolean). Arrays, String and classes are reference types.

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Neither statement is true. In a queue, insertion (enqueue) happens at the rear and deletion (dequeue) at the front.

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In a path graph the two end vertices have degree 1 and every other vertex has degree 2, so n − 2 vertices have degree 2.

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Demand-pull inflation happens when total demand exceeds supply and pulls prices up. Cost-push inflation comes from rising production costs.

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"r+" opens a file for reading and writing with the file pointer at the beginning. "a+" places it at the end; "rb" is read-only and "ab" append-only.

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A pandas Series is a one-dimensional labelled array that can hold any data type. A DataFrame is two-dimensional.

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A stack is LIFO: the last element pushed is the first popped. A queue is FIFO: the first element enqueued is the first dequeued.

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DFS goes as deep as possible along one branch before backtracking (using a stack). BFS visits all vertices at the current level before the next level (using a queue).

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Dictionary<TKey,TValue> is a .NET collection of key-value pairs, where values are looked up by a unique key.

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A static array's size is fixed at compile time. A dynamic array (created with malloc or realloc) can be resized at runtime.

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In a linear list, elements are arranged in a sequence where each has one successor. An array is the classic linear list. Trees and graphs are non-linear structures.

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The .NET Hashtable class stores key/value pairs and lets each element be accessed by its unique key using hashing. ArrayList and linked lists are accessed by index or position.