Arrays provide O(1) random access because we can calculate the memory address directly using: base + (index × size).

Stacks follow LIFO - the last element pushed is the first one popped, like a stack of plates.

Queues follow FIFO - documents are printed in the order they were submitted.

Linked lists allow O(1) insertion at the head - just create a new node and update the pointer. Arrays require shifting all elements.

BST property: left subtree contains smaller values, right subtree contains larger values.

In a balanced BST, we eliminate half the remaining nodes at each comparison, giving O(log n).

BFS uses a queue to explore all neighbors at the current level before moving deeper.

O(n²) means quadratic growth - if input doubles, time quadruples. Common in nested loops.

Stacks are perfect for undo - each action is pushed, and undo pops the most recent action (LIFO).

An adjacency matrix is a V×V 2D array, requiring O(V²) space regardless of the number of edges.