DSA interview questions for freshers

Place pointers at both ends

A slow pointer marks the end of the unique prefix

Walk both arrays with two indices and always append the smaller head into a result.

Two pointers skip non-letters/digits, compare lowercased characters, and stop on mismatch.

Dutch National Flag uses low, mid, and high pointers: swap 0s to the left, 2s to the right, and advance on 1s.

Sum the first k elements, then slide: add the incoming element and subtract the leaving one, tracking the max.

Maintain a running window sum as you slide by one, then divide by k for each position.

Keep a deque of indices of negatives inside the current window, dropping those that slide out of range.

Push opening brackets and pop when you see a matching closer

Store items in a list and treat the end as the top: append to push, pop from the end to pop, and peek the last index.

Scan tokens: push numbers, and for an operator pop two operands, apply it, and push the result.

Push every character, then pop them all into a new buffer.

A stack is LIFO and fits undo, DFS, matching brackets, and nested evaluation.

Push into an in-stack.

Start with "1" in a queue.

Walk with prev, curr, and next: save curr.next, point curr.next to prev, then advance prev and curr.

Slow pointer moves one step, fast moves two

Floyd's tortoise and hare: slow walks one, fast walks two

Advance a fast pointer n steps, then move fast and slow together until fast falls off

Copy the next node's value into the current node and bypass next by pointing current.next to next.next.