DSA Practice Sheet for Campus Placements

The journey from brute force to HashMap. The most common interview warm-up.

Track a running minimum and solve it in one pass.

Asked every season. The simplest form of DP.

Prefix and suffix products. Teaches you to think without division.

In-place array updates. A service-company coding round favourite.

Compare from both ends: strings and two pointers together.

Which pointer to move? You must explain the greedy reasoning.

Sort + two pointers + duplicate handling. Common in product interviews.

The left-max / right-max classic. Builds Hard-level confidence.

Character frequency counting with a size-26 array.

String comparison basics. Appears directly in online tests.

Your entry to sliding window: grow and shrink a window with a set/map.

Split, trim and reverse. Tests how you handle extra spaces.

The most direct use of a HashSet. A two-minute question.

What should the map key be: a sorted string or a count signature?

Frequency map + heap or bucket sort. A common follow-up.

A fixed-size window. The first step into sliding window.

A variable window: when to expand and when to shrink.

Window + frequency match. The next level of anagrams.

The number one stack question. Shows up at almost every company.

A design question: how do you keep the minimum in O(1)?

Monotonic stack: the next greater element pattern.

Pointer reversal. Know both the iterative and recursive versions.

Floyd's slow-fast pointers. Also asked in viva rounds.

The dummy node technique. The foundation of merge sort.

Find the middle in one pass. The simplest slow-fast use.

Heap + linked list. A product-company favourite Hard.

Your first recursive tree question. Learn the base case.

Swap left and right. Builds recursion confidence.

BFS with a queue. The template for many tree problems.

Use the BST property to decide: go left or right.

DFS on a grid. The easiest door into graphs.

Connected components. Very common at product companies.

Multi-source BFS: counting time as levels.

Cycle detection + topological sort. Directed graph basics.

Fibonacci-style DP. Go from recursion to a table.

Pick / not-pick DP. Many later problems build on this.

A form of unbounded knapsack: find the minimum coins.

O(n²) DP with an O(n log n) follow-up. Know both.

low, high, mid. Boundary mistakes happen most here.

Spotting which half is sorted is the whole problem.

Find the rotation point. Companion to the problem above.

Binary search on the answer. A new way of thinking.