The famous list, reorganized by pattern with the key insight for each problem — so you learn 15 ideas, not 75 answers.
The Blind 75 (a Facebook engineer's curated LeetCode list) endures
because it's the minimal set covering nearly every pattern interviews
draw from. Used wrong, it's 75 memorized solutions that evaporate under
pressure. Used right, it's ~15 patterns, each seen from 3–6 angles —
this page groups it that way, with the one-line insight per problem.
Protocol per problem: attempt 25–30 min cold → if stuck, read only the
insight here and try again → solved or not, say the approach out loud in
one sentence → log it for re-attempt in a week
(self-rate with the problem bank flashcards, schedule
via the study plan ). Marking "solved" after reading a
solution is the cardinal sin — re-derive, days later, or it didn't happen.
Problem The insight Two Sum dict of seen values → complement lookup, one pass Contains Duplicate set membership Product of Array Except Self prefix products × suffix products, no division Maximum Subarray Kadane: running sum, reset when it goes negative (1-D DP in disguise) Maximum Product Subarray track running max and min (negatives flip them) Top K Frequent count dict → bucket-by-frequency (or heap ) Group Anagrams canonical key: sorted word / letter counts Valid Anagram counting dict Longest Consecutive Sequence set + only start counting at left edges (x−1 absent) Encode/Decode Strings length-prefix framing — delimiters alone can't be safe
Problem The insight Valid Palindrome opposite ends, skip non-alphanumerics 3Sum sort; fix one, two-pointer the rest; skip duplicates carefully Container With Most Water move the shorter wall inward — exchange argument Trapping Rain Water water[i] = min(maxL, maxR) − h[i]; two pointers carry the maxes
Problem The insight Best Time to Buy/Sell Stock running min, best diff — window degenerates to one pass Longest Substring Without Repeating window + set; shrink from left past the repeat Longest Repeating Character Replacement window valid while (size − maxFreq) ≤ k Minimum Window Substring need/have counts; expand right, shrink left greedily
Problem The insight Valid Parentheses the canonical LIFO match
Problem The insight Search Rotated Sorted Array one half is always sorted — decide which, recurse into the right one Find Min in Rotated Sorted Array compare mid to right end; shrink toward the bend
Problem The insight Reverse Linked List the three-pointer dance, from memory, both directions of asking Merge Two Sorted Lists dummy head + two pointers Reorder List middle → reverse second half → interleave (three sub-skills) Remove Nth From End lead pointer n ahead, then move both Linked List Cycle Floyd fast/slow Merge K Sorted Lists heap of k heads — O(N log k)
Problem The insight Max Depth the 3-line recursion template Same Tree / Invert Tree simultaneous recursion / swap-and-recurse Subtree of Another Tree same-tree check at every node LCA of a BST walk from root until the targets split Validate BST (low, high) bounds passed down — child-check fails Level Order Traversal BFS queue, level = current queue length Kth Smallest in BST in-order traversal, count down Construct from Preorder + Inorder preorder[0] is root; inorder splits children Binary Tree Max Path Sum post-order: best one-leg path up vs best arch through Serialize/Deserialize preorder with null markers
Problem The insight Implement Trie children dict + end-flag Word Search II trie over dictionary guides grid backtracking — prune dead prefixes Design Add & Search Words '.' wildcard → branch into all children (DFS)
Problem The insight Find Median from Data Stream two heaps: max-heap lower half, min-heap upper, rebalance
Problem The insight Combination Sum choose/explore/un-choose; reuse allowed → don't advance index Word Search grid DFS + mark/unmark visited
Problem The insight Number of Islands flood fill (BFS/DFS) per unvisited land cell Clone Graph dict old→new while traversing Pacific Atlantic Water Flow reverse-flow BFS from both oceans; intersect Course Schedule cycle detection = topological sort (Kahn's / DFS colors) Graph Valid Tree connected + exactly n−1 edges (union-find ) Number of Connected Components union-find counting, or DFS sweeps Alien Dictionary build precedence edges from adjacent words → topo sort
Problem The insight Insert Interval three phases: before, merge-overlaps, after Merge Intervals sort by start; extend or push Non-overlapping Intervals max meetings kept (sort by end) → n − kept Meeting Rooms I / II overlap check / heap of end times
Problem The insight Climbing Stairs Fibonacci — the hello-world recurrence House Robber I / II take[i] vs skip[i]; circular → run twice excluding one end Coin Change min coins per amount, bottom-up (the greedy-fails poster child) Longest Increasing Subsequence O(n²) DP, or patience trick with binary search O(n log n) Word Break dp[i] = any dp[j] && s[j:i] in dict Decode Ways climbing stairs with validity conditions Palindromic Substrings / Longest Palindromic Substring expand around 2n−1 centers
Problem The insight Unique Paths grid[i][j] = top + left Longest Common Subsequence match → diag+1; else max(top, left)
Set/Clear bits family (Number of 1 Bits, Counting Bits, Missing Number,
Reverse Bits, Sum of Two Integers), Rotate Image (transpose + reverse
rows), Spiral Matrix (shrink four boundaries), Set Matrix Zeroes (first
row/col as markers).
The order that compounds
Do the groups top-to-bottom as listed — each reuses the previous (3Sum needs
two pointers; trees need recursion comfort; graphs need BFS from trees;
intervals need greedy). Two groups per week with re-attempts is a realistic
6-week pass; see the study plan for
scheduling, then graduate to mock drills .
You've 'done' the Blind 75 but blank in real interviews. What went wrong, and what's the fix? An interviewer gives a problem that isn't on any list. Walk me through the first 5 minutes. The page is the practice. Track group-by-group; when all groups are
green twice, you're ready for mock drills — the last
step before the real thing.