Define data structure and its importance

A data structure is a particular way of organising and storing data in the memory of a computer so that it can be accessed, searched and modified efficiently. It also includes the set of operations defined on the organised data. Examples: array, stack, queue, linked list, tree, graph.

Importance of data structures

1. Efficient data handling: the right structure makes searching, insertion and deletion fast (e.g., a hash table or binary search tree searches faster than an unsorted array).
2. Efficient use of memory: data is stored in a compact or flexible way (linked lists grow and shrink as needed).
3. Reusability and abstraction: a structure such as a stack or queue is written once and reused in many programs; users need not know its internals.
4. Solving complex problems: expression evaluation (stack), scheduling (queue), file systems (tree), road maps and networks (graph).
5. Better algorithm design: running time of an algorithm depends largely on the structure it uses, so choosing it well reduces time and space complexity.
6. Manageable programs: organised data makes large software easier to design, test and maintain.

In short, a program is data structures + algorithms (Wirth); a poor data structure makes even a good algorithm slow.