0600 - 0699
Solutions categorised by Problem IDs
605 - Can Place FlowersDetermine how many flowers fit in a flowerbed while keeping at least one empty plot between adjacent plantings.606 - Construct String from Binary TreeEncode a binary tree as a parenthesized preorder string and retain the empty child markers needed to preserve its structure.609 - Find Duplicate File in SystemFind duplicate files by parsing directory entries and grouping file paths that share identical contents.621 - Task SchedulerMinimize task scheduling time under a cooldown by reasoning about task frequencies or simulating available tasks with a heap.622 - Design Circular QueueImplement a circular queue in an array by wrapping the front and rear positions around its fixed capacity.623 - Add One Row to TreeInsert a row at a specified tree depth by attaching new nodes and reconnecting the original children beneath them.633 - Sum of Square NumbersCheck whether a nonnegative integer is a sum of two squares by testing candidate squares with binary search.637 - Average of Levels in Binary TreeCompute the average node value at each level of a binary tree by processing levels with breadth-first search.645 - Set MismatchIdentify the duplicated and missing values in a sequence using counts, sorting, arithmetic, or XOR.647 - Palindromic SubstringsCount palindromic substrings with Manacher's algorithm by using the palindrome radius at each center.650 - 2 Keys KeyboardMinimize Copy All and Paste operations by factoring the desired number of characters into multiplicative steps.653 - Two Sum IV - Input is a BSTCheck whether two nodes in a binary search tree sum to a target by searching for complementary values during traversal.662 - Maximum Width of Binary TreeMeasure each level's width, including gaps, by assigning tree positions during breadth-first traversal.678 - Valid Parenthesis StringValidate parentheses with wildcards by tracking the minimum and maximum possible number of unmatched opening brackets.680 - Valid Palindrome IICheck whether a string can be a palindrome after deleting at most one character by testing possible removals.682 - Baseball GameSimulate a baseball score record by updating earlier scores when cancellation, doubling, or sum operations appear.684 - Redundant ConnectionFind the extra edge in an undirected graph by detecting when its endpoints already belong to the same disjoint set.692 - Top K Frequent WordsSelect the k most frequent words, breaking frequency ties in alphabetical order, with a heap or frequency buckets.695 - Max Area of IslandFind the largest island area by exploring each connected group of land cells and counting its size.698 - Partition to K Equal Sum SubsetsDecide whether the array can be split into k equal-sum subsets by tracking valid partial partitions with dynamic programming.
