https://k5kc.com/ Recent content on K5kC | Code & More Next.js en-us Sat, 07 Feb 2026 20:14:04 GMT https://k5kc.com/cs/problems/course-schedule-1-is-it-possible https://k5kc.com/cs/problems/course-schedule-1-is-it-possible Sat, 07 Feb 2026 13:43:00 GMT ## Problem There are a total of `numCourses` courses you have to take, labeled from `0` to `numCourses - 1`. You are given an array `prerequisites` where `prerequisites[i] = [ai, bi]` indicates that https://k5kc.com/cs/problems/clone-undirected-graph https://k5kc.com/cs/problems/clone-undirected-graph Sat, 07 Feb 2026 13:33:00 GMT ## Problem Given a reference of a node in a **[connected](https://en.wikipedia.org/wiki/Connectivity_(graph_theory)#Connected_graph)** undirected graph. Return a [**deep copy**](https://en.wikipedi https://k5kc.com/cs/problems/valid-parentheses https://k5kc.com/cs/problems/valid-parentheses Sat, 07 Feb 2026 07:31:00 GMT ## Problem Given a string `s` containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid. An input string is valid if: 1. Open brackets must https://k5kc.com/cs/problems/alien-dictionary https://k5kc.com/cs/problems/alien-dictionary Sun, 01 Feb 2026 22:15:00 GMT ## Problem **Gist:** Given a sorted dictionary (array of words) of an alien language, find order of characters in the language. **Detailed:** There is a new alien language which uses the latin alph https://k5kc.com/cs/problems/pacific-atlantic-water-flow https://k5kc.com/cs/problems/pacific-atlantic-water-flow Mon, 19 Jan 2026 00:48:00 GMT ## Problem There is an `m x n` rectangular island that borders both the **Pacific Ocean** and **Atlantic Ocean**. The **Pacific Ocean** touches the island's left and top edges, and the **Atlantic Oc https://k5kc.com/cs/problems/graph-valid-tree https://k5kc.com/cs/problems/graph-valid-tree Sat, 10 Jan 2026 06:52:00 GMT ## Problem Given `n` nodes labeled from `0` to `n-1` and a list of undirected edges (each edge is a pair of nodes), write a function to check whether these edges make up a valid tree. ### Examples https://k5kc.com/cs/problems/happy-number https://k5kc.com/cs/problems/happy-number Mon, 05 Jan 2026 00:32:00 GMT ## Problem Write an algorithm to determine if a number is "happy". ### Definition A **happy number** is a number defined by the following process: - Starting with any positive integer, replace th https://k5kc.com/cs/problems/open-the-lock https://k5kc.com/cs/problems/open-the-lock Mon, 05 Jan 2026 00:28:00 GMT ## Problem You have a lock in front of you with 4 circular wheels. Each wheel has 10 slots: `'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'`. The wheels can rotate freely and wrap around: for exam https://k5kc.com/cs/problems/seat-reservation-manager https://k5kc.com/cs/problems/seat-reservation-manager Mon, 05 Jan 2026 00:24:00 GMT ## Problem Design a system that manages the reservation state of `n` seats that are numbered from `1` to `n`. Implement the `SeatManager` class: - `SeatManager(int n)` Initializes a `SeatManager`  https://k5kc.com/cs/problems/convert-sorted-array-to-height-balanced-binary-search-tree https://k5kc.com/cs/problems/convert-sorted-array-to-height-balanced-binary-search-tree Mon, 05 Jan 2026 00:22:00 GMT ## Problem Given an integer array `nums` where the elements are sorted in **ascending order**, convert _it to a **height-balanced** binary search tree_. ### Examples **Example 1:** ```d Input: nu https://k5kc.com/cs/problems/palindrome-linked-list https://k5kc.com/cs/problems/palindrome-linked-list Mon, 05 Jan 2026 00:16:00 GMT ## Problem Given the `head` of a singly linked list, return `true` if it is a [palindrome]({{< relref "/gk/algorithms/palindrome-definition.md" >}}) _or_ `false` otherwise. ### Examples **Example https://k5kc.com/cs/problems/remove-linked-list-elements https://k5kc.com/cs/problems/remove-linked-list-elements Mon, 05 Jan 2026 00:16:00 GMT ## Problem Remove all elements from a linked list of integers that have value val. ### Examples **Example 1:** ```d Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6 Return: 1 --> 2 --> 3 --> https://k5kc.com/cs/problems/capacity-to-ship-packages-within-d-days https://k5kc.com/cs/problems/capacity-to-ship-packages-within-d-days Mon, 05 Jan 2026 00:13:00 GMT ## Problem A conveyor belt has packages that must be shipped from one port to another within `days` days. The `ith` package on the conveyor belt has a weight of `weights[i]`. Each day, we load the https://k5kc.com/cs/problems/single-element-in-a-sorted-array https://k5kc.com/cs/problems/single-element-in-a-sorted-array Mon, 05 Jan 2026 00:13:00 GMT ## Problem You are given a sorted array consisting of only integers where every element appears exactly twice, except for one element which appears exactly once. Return _the single element that app https://k5kc.com/cs/problems/asteroid-collision https://k5kc.com/cs/problems/asteroid-collision Mon, 05 Jan 2026 00:11:00 GMT ## Problem We are given an array `asteroids` of integers representing asteroids in a row. For each asteroid, the absolute value represents its size, and the sign represents its direction (positive https://k5kc.com/cs/problems/binary-tree-level-order-traversal https://k5kc.com/cs/problems/binary-tree-level-order-traversal Sun, 04 Jan 2026 21:53:00 GMT ## Problem Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level). ### Examples **Example 1:** ```mermaid graph TD; 3 --> 9 & 20 https://k5kc.com/cs/problems/implement-trie https://k5kc.com/cs/problems/implement-trie Sun, 04 Jan 2026 21:23:00 GMT ## Problem A [**trie**](https://en.wikipedia.org/wiki/Trie) (pronounced as "try") or **prefix tree** is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. The https://k5kc.com/cs/problems/detect-squares https://k5kc.com/cs/problems/detect-squares Sun, 04 Jan 2026 21:15:00 GMT ## Problem You are given a stream of points on the X-Y plane. Design an algorithm that: - **Adds** new points from the stream into a data structure. **Duplicate** points are allowed and should be t https://k5kc.com/cs/problems/multiply-strings https://k5kc.com/cs/problems/multiply-strings Sun, 04 Jan 2026 21:15:00 GMT ## Problem Given two non-negative integers `num1` and `num2` represented as strings, return the product of `num1` and `num2`, also represented as a string. **Note:** You must not use any built-in B https://k5kc.com/cs/problems/roman-to-integer https://k5kc.com/cs/problems/roman-to-integer Sun, 04 Jan 2026 21:15:00 GMT ## Problem [Roman numerals]({{< relref "roman-numerals.md" >}}) Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999. ### Examples **Example https://k5kc.com/cs/problems/implement-power-function-1 https://k5kc.com/cs/problems/implement-power-function-1 Sun, 04 Jan 2026 21:14:00 GMT ## Problem Implement [pow(x, n)](http://www.cplusplus.com/reference/valarray/pow/), which calculates `x` raised to the power `n` (i.e., `x^n`). ### Examples **Example 1:** ```d Input: x = 2.00000 https://k5kc.com/cs/problems/plus-one-1-given-number-as-array-plus-one https://k5kc.com/cs/problems/plus-one-1-given-number-as-array-plus-one Sun, 04 Jan 2026 21:14:00 GMT ## Problem Given a non-negative number represented as an array of digits, plus one to the number. The digits are stored such that the most significant digit is at the head of the list. ### Examples https://k5kc.com/cs/problems/add-binary-strings https://k5kc.com/cs/problems/add-binary-strings Sun, 04 Jan 2026 21:12:00 GMT ## Problem Given two binary strings `a` and `b`, return _their sum as a binary string_. ### Examples **Example 1:** ```d Input: a = "11", b = "1" Output: "100" ``` **Example 2:** ```d Input: a https://k5kc.com/cs/problems/reverse-integer https://k5kc.com/cs/problems/reverse-integer Sun, 04 Jan 2026 21:12:00 GMT ## Problem Given a signed 32-bit integer `x`, return `x` _with its digits reversed_. If reversing `x` causes the value to go outside the signed 32-bit integer range `[-2^31, 2^31 - 1]`, then return  https://k5kc.com/cs/problems/summary-ranges https://k5kc.com/cs/problems/summary-ranges Sun, 04 Jan 2026 21:10:00 GMT ## Problem You are given a **sorted unique** integer array `nums`. A **range** `[a,b]` is the set of all integers from `a` to `b` (inclusive). Return _the **smallest sorted** list of ranges that * https://k5kc.com/cs/problems/merge-triplets-to-form-target-triplet https://k5kc.com/cs/problems/merge-triplets-to-form-target-triplet Sun, 04 Jan 2026 21:09:00 GMT ## Problem A **triplet** is an array of three integers. You are given a 2D integer array `triplets`, where `triplets[i] = [ai, bi, ci]` describes the `ith` **triplet**. You are also given an integer https://k5kc.com/cs/problems/partition-labels https://k5kc.com/cs/problems/partition-labels Sun, 04 Jan 2026 21:09:00 GMT ## Problem You are given a string `s`. We want to partition the string into as many parts as possible so that each letter appears in at most one part. Note that the partition is done so that after https://k5kc.com/cs/problems/valid-parenthesis-string https://k5kc.com/cs/problems/valid-parenthesis-string Sun, 04 Jan 2026 21:09:00 GMT ## Problem Given a string `s` containing only three types of characters: `'('`, `')'` and `'*'`, return `true` _if_ `s` _is **valid**_. The following rules define a **valid** string: - Any left pa https://k5kc.com/cs/problems/hand-of-straights https://k5kc.com/cs/problems/hand-of-straights Sun, 04 Jan 2026 21:08:00 GMT ## Problem Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size `groupSize`, and consists of `groupSize` consecutive cards. Given an integer https://k5kc.com/cs/problems/jump-game-2-get-min-jumps https://k5kc.com/cs/problems/jump-game-2-get-min-jumps Sun, 04 Jan 2026 21:08:00 GMT ## Problem Given an array of non-negative integers `nums`, you are initially positioned at the first index of the array. Each element in the array represents your maximum jump length at that positi https://k5kc.com/cs/problems/burst-balloons https://k5kc.com/cs/problems/burst-balloons Sun, 04 Jan 2026 21:06:00 GMT ## Problem You are given `n` balloons, indexed from `0` to `n - 1`. Each balloon is painted with a number on it represented by an array `nums`. You are asked to burst all the balloons. If you burst https://k5kc.com/cs/problems/distinct-subsequences https://k5kc.com/cs/problems/distinct-subsequences Sun, 04 Jan 2026 21:06:00 GMT ## Problem Given two strings s and t, return _the number of distinct_ **_subsequences_** _of_ s _which equals_ t. The test cases are generated so that the answer fits on a 32-bit signed integer. # https://k5kc.com/cs/problems/regular-expression-matching https://k5kc.com/cs/problems/regular-expression-matching Sun, 04 Jan 2026 21:06:00 GMT ## Problem Given an input string `s` and a pattern `p`, implement regular expression matching with support for `'.'` and `'*'` where: - `'.'` Matches any single character. - `'*'` Matches zero or m https://k5kc.com/cs/problems/interleaving-string https://k5kc.com/cs/problems/interleaving-string Sun, 04 Jan 2026 21:05:00 GMT ## Problem Given strings `s1`, `s2`, and `s3`, find whether `s3` is formed by an **interleaving** of `s1` and `s2`. An **interleaving** of two strings `s` and `t` is a configuration where they are https://k5kc.com/cs/problems/longest-increasing-path-in-a-matrix https://k5kc.com/cs/problems/longest-increasing-path-in-a-matrix Sun, 04 Jan 2026 21:05:00 GMT ## Problem Given an `m x n` integers `matrix`, return _the length of the longest increasing path in_ `matrix`. From each cell, you can either move in four directions: left, right, up, or down. You  https://k5kc.com/cs/problems/target-sum https://k5kc.com/cs/problems/target-sum Sun, 04 Jan 2026 21:05:00 GMT ## Problem You are given an integer array `nums` and an integer `target`. You want to build an **expression** out of nums by adding one of the symbols `'+'` and `'-'` before each integer in nums an https://k5kc.com/cs/problems/best-time-to-buy-and-sell-stock-with-cooldown https://k5kc.com/cs/problems/best-time-to-buy-and-sell-stock-with-cooldown Sun, 04 Jan 2026 21:04:00 GMT ## Problem # Problem Definition You are given an array `prices` where `prices[i]` is the price of a given stock on the `ith` day. Find the maximum profit you can achieve. You may complete as many https://k5kc.com/cs/problems/min-cost-climbing-stairs https://k5kc.com/cs/problems/min-cost-climbing-stairs Sun, 04 Jan 2026 21:03:00 GMT ## Problem You are given an integer array `cost` where `cost[i]` is the cost of `ith` step on a staircase. Once you pay the cost, you can either climb one or two steps. You can either start from th https://k5kc.com/cs/problems/swim-in-rising-water https://k5kc.com/cs/problems/swim-in-rising-water Sun, 04 Jan 2026 21:02:00 GMT ## Problem You are given an `n x n` integer matrix `grid` where each value `grid[i][j]` represents the elevation at that point `(i, j)`. The rain starts to fall. At time `t`, the depth of the water https://k5kc.com/cs/problems/network-delay-time https://k5kc.com/cs/problems/network-delay-time Sun, 04 Jan 2026 21:01:00 GMT ## Problem You are given a network of `n` nodes, labeled from `1` to `n`. You are also given `times`, a list of travel times as directed edges `times[i] = (ui, vi, wi)`, where `ui` is the source nod https://k5kc.com/cs/problems/min-cost-to-connect-all-points https://k5kc.com/cs/problems/min-cost-to-connect-all-points Sun, 04 Jan 2026 21:00:00 GMT ## Problem You are given an array `points` representing integer coordinates of some points on a 2D-plane, where `points[i] = [xi, yi]`. The cost of connecting two points `[xi, yi]` and `[xj, yj]` i https://k5kc.com/cs/problems/course-schedule-2-get-ordered-courses https://k5kc.com/cs/problems/course-schedule-2-get-ordered-courses Sun, 04 Jan 2026 20:57:00 GMT ## Problem There are a total of `numCourses` courses you have to take, labeled from `0` to `numCourses - 1`. You are given an array `prerequisites` where `prerequisites[i] = [ai, bi]` indicates that https://k5kc.com/cs/problems/rotting-oranges https://k5kc.com/cs/problems/rotting-oranges Sun, 04 Jan 2026 20:56:00 GMT ## Problem You are given an `m x n` `grid` where each cell can have one of three values: - `0` representing an empty cell, - `1` representing a fresh orange, or - `2` representing a rotten orange. https://k5kc.com/cs/problems/surrounded-regions https://k5kc.com/cs/problems/surrounded-regions Sun, 04 Jan 2026 20:56:00 GMT ## Problem # Surrounded Regions Given an `m x n` matrix `board` containing `'X'` and `'O'`, _capture all regions that are 4-directionally surrounded by_ `'X'`. A region is **captured** by flipping https://k5kc.com/cs/problems/walls-and-gates https://k5kc.com/cs/problems/walls-and-gates Sun, 04 Jan 2026 20:56:00 GMT ## Problem # Problem You are given an `m x n` grid `rooms` initialized with these three possible values. - `-1` A wall or an obstacle. - `0` A gate. - `INF` Infinity means an empty room. We use th https://k5kc.com/cs/problems/max-area-of-island https://k5kc.com/cs/problems/max-area-of-island Sun, 04 Jan 2026 20:55:00 GMT ## Problem You are given an `m x n` binary matrix `grid`. An island is a group of `1`'s (representing land) connected **4-directionally** (horizontal or vertical.) You may assume all four edges of t https://k5kc.com/cs/problems/number-of-islands https://k5kc.com/cs/problems/number-of-islands Sun, 04 Jan 2026 20:55:00 GMT ## Problem Given an `m x n` 2D binary grid `grid` which represents a map of `'1'`s (land) and `'0'`s (water), return _the number of islands_. An **island** is surrounded by water and is formed by c https://k5kc.com/cs/problems/letter-combinations-of-a-phone-number https://k5kc.com/cs/problems/letter-combinations-of-a-phone-number Sun, 04 Jan 2026 20:54:00 GMT ## Problem Given a string containing digits from `2-9` inclusive, return all possible letter combinations that the number could represent. Return the answer in **any order**. A mapping of digit to https://k5kc.com/cs/problems/n-queens https://k5kc.com/cs/problems/n-queens Sun, 04 Jan 2026 20:54:00 GMT ## Problem The **n-queens** puzzle is the problem of placing `n` queens on an `n x n` chessboard such that no two queens attack each other. Given an integer `n`, return _all distinct solutions to t https://k5kc.com/cs/problems/palindrome-partitioning https://k5kc.com/cs/problems/palindrome-partitioning Sun, 04 Jan 2026 20:54:00 GMT ## Problem > Given a string `s`, partition `s` such that every substring of the partition is a **palindrome**. Return all possible palindrome partitioning of `s`. ### Definition [Palindrome Defini