Problems¶
Individual problems worked through: the observation that cracks it, the solution, and where I went wrong first. Newest first within each judge.
CodeChef¶
- Starters 81 — Beautiful Strings: the DP state I didn’t need · 26 Sep 2026
- Starters 81 — Good XOR: the case I ruled out with a parity argument · 26 Sep 2026
- FALLPR — Fall Prevention: I deleted the wrong element · 24 Sep 2026
- SHSC — Shift Score: I reached for rerooting when counting edges was enough · 24 Sep 2026
- Starters 84 — SUM OR: a correct digit DP that still TLEs · 21 Sep 2026
- Starters 86 — Minimum Operation: the case my gut missed · 16 Sep 2026
- Starters 87 — Count the Permutations (always) · 15 Sep 2026
- Starters 88 — Chef and Good Array: pairs are intervals · 14 Sep 2026
- Starters 88 — Minimize the Bits: the one I couldn’t solve · 14 Sep 2026
- Starters 89 — Two Averages: fix the total, then split it · 12 Sep 2026
- Starters 90 — Minimum Ugliness: the diameter of a subset · 9 Sep 2026
- Starters 93 — Greedy: the problem is called Greedy and the answer is a DP · 5 Sep 2026
- Starters 93 — Thank U, Next: dijkstra on energy graph · 5 Sep 2026
- Starters 95 — Break This Array: the cut probability I kept forgetting · 2 Sep 2026
- Starters 96 — Zero Array: when the last equation is the whole problem · 1 Sep 2026
- Starters 97 — Triplets Min: the binary search that collapses into a prefix sum · 31 Aug 2026
- Starters 253 — Dis-Card: my dominance count was off by one, and off by a lot · 27 Aug 2026
- Starters 253 — Flower Reversal: only the two boundaries move · 27 Aug 2026
- Starters 253 — Grid Jump: I assumed the answer sits at a corner · 27 Aug 2026
- Starters 117 — Equality Etiquette: the sign choice is the whole problem · 26 Aug 2026
- Starters 116 — Expected Diameter: two extra nodes and the vertices that matter · 25 Aug 2026
- Starters 252 — Tree Counting: a parity invariant, Scoins’ formula, and a DP state I got wrong · 19 Aug 2026
- Starters 108 — Clan Expansion: the largest gap between sources · 12 Aug 2026
- Starters 106 — Reach Anywhere: finding shortest odd and even parity distances · 7 Aug 2026
- Starters 250 — Subsequence 1: Chains, not cuts · 6 Aug 2026
- Starters 250 — Subsequence 2: Counting windows, one threshold at a time · 6 Aug 2026
- Starters 105 — Wishcraft · 3 Aug 2026
- Starters 115 — Make All Zero: Only Prefix Minima Can Be Eliminated · 24 Jul 2026
- Starters 248 — Deleting Elements (Easy) · 22 Jul 2026
- Starters 248 — Merging Parity · 22 Jul 2026
- Starters 247 — Fair Flipping (Easy): What This Constructive Proof Taught Me · 16 Jul 2026
- Starters 247 — Red Blue Swaps: From Swaps to Buckets (A DP Pattern) · 16 Jul 2026
LeetCode¶
- Weekly Contest 516 — Valid K-Unique Subarrays I: Mo’s algorithm, and where the √N actually comes from · 23 Aug 2026
- Weekly Contest 515 — Elevator Requests III: Held–Karp, a poisoned sentinel, and a duplicate-floor scare · 17 Aug 2026
- Weekly Contest 515 — Maximum Gap Between Stations: greedy extremes, and the max-of-max trap · 17 Aug 2026
- Weekly Contest 514 — Maximum Area of Two Non-Overlapping Square Submatrices: only the extremes can witness a valid pair · 9 Aug 2026
- Biweekly 188 — Fence Width Optimization: From O(n³) to O(n²) · 1 Aug 2026
- Biweekly 188 — Minimum Possible Maximum Waiting Time · 1 Aug 2026
- Weekly 509 — Palindromic Subarray Sum with Rolling Hashes · 5 Jul 2026
- Weekly 509 — Subsequence After One Replacement: Did You Consume the Matched Character? · 5 Jul 2026
- Biweekly 186 — Count Distinct Ways to Form Target from Two Strings · 4 Jul 2026
Codeforces¶
- Round 2239 D1 — XOR Sorting (Easy) · 21 Jul 2026
- Round 1103 (Div. 3) E — Friendly Gifts: Disjoint Value Intervals · 18 Jul 2026
- Round 1103 (Div. 3) F2 — Elections in Saransk (Hard Version): Sum-minus-Max DP · 17 Jul 2026
- Round 267 (Div. 2) C — George and Job: DP on Fixed-Length Segments · 17 Jul 2026
- Round 1103 (Div. 3) F1 — Elections in Saransk (Easy Version): Prime-wise Counting · 10 Jul 2026
- Round 179 (Div. 1) B — Greg and Graph: Learning to Think in Reverse · 9 Jul 2026
- Edu Round 192 D — From Merging Digits to Longest Common Subsequence · 7 Jul 2026
- Edu Round 192 B — A Small Algebra Trick That Turns an O(n²) Idea into O(n) · 7 Jul 2026
AtCoder¶
- ABC 476 D — Automat: equal money, unequal wallets · 20 Sep 2026
- ABC472 E — Odd Cycle: depth parity, and two bugs in reconstructing the cycle · 23 Aug 2026
- ABC471 D — Chargers: subtract the common term · 16 Aug 2026
- ARC226 A — Meeting Division: when the constraint is the solution · 10 Aug 2026
- ABC470 C — Inc, Dec, Xor: the “pay with tokens you already minted” trick · 8 Aug 2026
- ABC469 E — Pro Exam Eligibility · 1 Aug 2026
- ABC466 C — Count Close Pairs · 14 Jul 2026
Repovive¶
- Starter Round 4 C — Corner Meeting: Minimizing the Max of an Increasing and a Decreasing Function · 6 Jul 2026
- Starter Round 4 D — Distant Transfers: Deriving Invariants Instead of Constructing Moves · 6 Jul 2026