DSA Practice

Practice data structures and algorithms by pattern — arrays, two pointers, sliding window, trees and graphs.

See the whole map.

Meet every essential data structure and pattern through one small, friendly win at a time.

• Running Sum of 1D Array — Carry one useful value forward · Warm-up
• Contains Duplicate — Remember what you have seen · Warm-up
• Two Sum — Look up the missing complement · Easy
• Valid Palindrome — Shrink from both ends · Easy
• Maximum Average Subarray I — Reuse a fixed-size window · Easy
• Range Sum Query — Immutable — Precompute once, answer many times · Easy
• Valid Parentheses — Last opened, first closed · Easy
• Reverse Linked List — Preserve the next node before rewiring · Easy
• Binary Search — Discard half using a sorted invariant · Easy
• Fibonacci Number — Define a small base case, then a smaller version · Warm-up
• Maximum Depth of Binary Tree — A node asks its children a smaller question · Easy
• Average of Levels in Binary Tree — Process neighbours layer by layer · Easy
• Last Stone Weight — Repeatedly take the most important item · Easy
• Flood Fill — Visit connected neighbours safely · Easy
• Find if Path Exists in Graph — Explore a frontier until you reach the goal · Easy
• Assign Cookies — Make the locally safe choice · Easy
• Meeting Overlap Check — Sort by start, compare with the last end · Warm-up
• Subsets — Choose, explore, unchoose · Stretch
• Climbing Stairs — Remember repeated smaller answers · Easy
• Single Number — Use XOR cancellation · Easy
• Autocomplete Starter — Share prefixes as a tree · Stretch

Connect the dots.

Return to each idea only when it has something new to teach you. No endless repetitions.

• Group Anagrams — Map many values to one signature · Easy
• Container With Most Water — Move the limiting side · Stretch
• Longest Substring Without Repeating Characters — Grow, then repair a variable window · Stretch
• Subarray Sum Equals K — Look up an earlier prefix · Stretch
• Min Stack — Store an answer alongside each item · Easy
• Daily Temperatures — Keep unresolved candidates ordered · Stretch
• Merge Two Sorted Lists — Build with a moving tail · Easy
• Linked List Cycle — Fast and slow pointers · Easy
• Search Insert Position — Search for the first valid position · Easy
• Koko Eating Bananas — Binary search the answer · Stretch
• Same Tree — Compare matching recursive structure · Easy
• Binary Tree Level Order Traversal — Collect one queue layer at a time · Easy
• Validate Binary Search Tree — Carry valid bounds downward · Stretch
• Kth Largest Element in an Array — Keep only the k most relevant values · Stretch
• Number of Islands — Start a traversal once per new component · Stretch
• Course Schedule — Track visiting and visited states · Stretch
• Redundant Connection — Merge groups and detect an existing connection · Stretch
• Insert Interval — Before, merge, after · Stretch
• Jump Game — Track the furthest safe reach · Stretch
• Permutations — Choose an unused option at each depth · Stretch
• House Robber — Take or skip with a small state · Easy
• Coin Change — Build the best answer for every smaller amount · Stretch
• Unique Paths — Build a grid from top and left · Easy
• Implement Trie (Prefix Tree) — Traverse character choices consistently · Stretch
• Counting Bits — Reuse the answer after removing one bit · Easy

Recognise and explain.

Meet familiar patterns in a mixed order, then practise the words you would use in an interview.

• Top K Frequent Elements — Count, then keep the best k · Stretch
• Product of Array Except Self — Carry information from both directions · Stretch
• 3Sum — Fix one value, solve a two-sum range · Stretch
• Longest Repeating Character Replacement — Keep a window valid under a budget · Stretch
• Decode String — Save outer context before nested work · Stretch
• Add Two Numbers — Advance two lists with a carry · Easy
• Lowest Common Ancestor of a BST — Use ordering to choose one branch · Easy
• Rotting Oranges — Expand one minute at a time · Stretch
• Pacific Atlantic Water Flow — Search backwards from both destinations · Stretch
• Combination Sum — Choose with a remaining target · Stretch
• Word Break — Mark reachable string boundaries · Stretch
• Time Based Key-Value Store — Search the latest valid timestamp · Stretch