Daily Problem of the Day breakdowns, dry runs, and verified Java / JavaScript implementations.
Difficulty: Medium | Date: 2026-09-17
Find two non-overlapping sub-arrays each with sum equal to target minimizing their combined length using sliding window and prefix dynamic programming.
Difficulty: Medium | Date: 2026-09-16
Count the number of ways to draw k non-overlapping line segments over n points using prefix-sum optimized 2D dynamic programming.
Difficulty: Hard | Date: 2026-09-15
Find the maximum number of non-overlapping palindromic substrings of length at least k using 2D palindrome precomputation and a greedy-pruned prefix dynamic programming transition.
Difficulty: Medium | Date: 2026-09-14
Find the translation of one binary grid that maximizes overlapping 1s using shift vector enumeration and hash map frequency voting.
Difficulty: Easy | Date: 2026-09-14
Determine whether two axis-aligned rectangles overlap with positive area by decomposing 2D geometry into independent 1D interval overlap checks.
Difficulty: Easy | Date: 2026-09-11
Count the number of distinct 3-digit even numbers without leading zeros that can be formed from an array of digits using position enumeration and hash set deduplication.
Difficulty: Medium | Date: 2026-09-10
Count how many nodes in a binary tree have a value equal to the rounded-down average of their subtree using a single post-order recursive traversal.
Difficulty: Medium | Date: 2026-09-08
Count the total number of commas across standard-formatted integers from 1 to n for massive constraints (up to 10^15) using 64-bit integer range grouping.
Difficulty: Easy | Date: 2026-09-08
Count the total number of commas across standard-formatted integers from 1 to n using digit grouping and mathematical division.
Difficulty: Hard | Date: 2026-09-07
Count the number of distinct non-empty subsequences of a string modulo 10^9 + 7 using 1D dynamic programming and a 26-letter running count replace strategy.
Difficulty: Hard | Date: 2026-09-07
Count how many distinct subsequences of string s equal string t using 2D dynamic programming, recursion with memoization, and space-optimized table filling.
Difficulty: Easy | Date: 2026-09-05
Find the smallest index where the maximum of all elements from the start minus the minimum of all elements to the end is at most k using prefix max and suffix min precomputations.
Difficulty: Medium | Date: 2026-09-05
Find the smallest index where the maximum of all elements from the start minus the minimum of all elements to the end is at most k with large constraints (N up to 100,000) using prefix max and suffix min precomputation.
Difficulty: Medium | Date: 2026-09-04
Determine if an array can be transformed into a uniform parity array when you can only subtract strictly smaller elements. Explains the forced minimum logic and parity rules.
Difficulty: Easy | Date: 2026-09-03
Determine if an array can be transformed into a uniform parity array by keeping or subtracting other elements. Explains the mathematical proof showing why the answer is always true.
Difficulty: Hard | Date: 2026-09-01
Find the minimum total number of moves needed to collect all litter in a grid classroom using state-space BFS with bitmasks and energy tracking.
Difficulty: Medium | Date: 2026-08-31
Find the minimum and maximum distance between critical points (local maxima/minima) in a linked list in a single pass.
Difficulty: Medium | Date: 2026-08-30
Find the minimum number of deletions from the front or back of an array to remove both the minimum and maximum elements.
Difficulty: Medium | Date: 2026-08-29
Learn how to find the lexicographically smallest array reachable by swapping elements with difference less than or equal to a limit using sorting and Union-Find.
Difficulty: Hard | Date: August 28, 2026
Solve the Hard challenge of building the smallest lexicographical palindrome permutation greater than target.