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LeetCode problem #1130

LeetCode problem #2816

LeetCode problem #134

LeetCode problem #827

LeetCode problem #1774

LeetCode problem #1300

Find maximum value that can be obtained with given weight capacity

Add two numbers represented as linked lists where digits are stored in reverse order

Given a sorted array of integers and a target value, return the index of the target if found, or -1 if not present.

Traverse a binary tree in inorder (left -> root -> right)

Traverse a binary tree in preorder (root -> left -> right)

Traverse the boundary of a binary tree in anti-clockwise direction.

Learn BFS traversal with a FIFO queue + visited set. Includes BFS pseudocode, example, and O(V+E) complexity—practice for FAANG interviews.

Find the maximum profit from buying and selling stock with at most one transaction

Distribute the minimum number of candies to children in a line such that each child gets at least one and children with higher ratings get more than their neighbors

Find the celebrity in a party of n people using the minimum number of questions.

Determine if a string reads the same forwards and backwards, ignoring case and non-alphanumeric characters.

Determine if one string is a rotation of another string by checking if it can be formed by rotating the characters.

Detect if a linked list has a cycle and find the starting point of the cycle

Find the minimum number of coins needed to make a given amount

Medium DP/unbounded knapsack: dp[x]+=dp[x-c] counts coin change ways (no permutations). O(n·amount) time, O(amount) space. Practice now.

Given an array of distinct integers and a target, return all unique combinations where the chosen numbers sum to target (elements may be reused)

Construct a binary tree from preorder and inorder traversal sequences.

Convert a sorted array to a height-balanced binary search tree.

Create a deep copy of a linked list where each node has a random pointer

Generate the nth term of the count-and-say sequence.

Count the number of nodes in a binary tree where the path from root to that node has no nodes with values greater than the current node.

Find the number of days until a warmer temperature for each day.

Decode a string encoded with the format k[encoded_string].

Design a circular queue with fixed size that supports enqueue, dequeue, front, rear, isEmpty, and isFull operations.

Determine if a directed graph contains a cycle

Detect if a linked list has a cycle using Floyd's cycle detection algorithm

Learn graph cycle detection in an undirected graph using DFS/BFS parent tracking or Union-Find (DSU). O(V+E). Step-by-step—practice now.

Find the diameter (longest path) of a binary tree.

Find minimum operations to convert one string to another

Find the minimum number of operations (insert, delete, replace) required to transform one string into another.

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Evaluate mathematical expressions with proper operator precedence and parentheses.

Calculate the nth Fibonacci number using dynamic programming

Find the majority element that appears more than n/2 times using Boyer-Moore majority vote algorithm

Find the middle node of a linked list using the two-pointer technique

Find the missing number in an array containing n distinct numbers taken from 1, 2, 3, ..., n+1

Find the first non-repeating character in a string and return its index.

Flatten a binary tree into a linked list in-place using preorder traversal.

Flatten a multilevel doubly linked list into a single level

Generate all possible permutations of a given string.

Given an array of strings, group the anagrams together.

Group strings that are anagrams of each other together.

Find maximum amount that can be robbed without robbing adjacent houses

Implement a queue using arrays or linked lists with O(1) time complexity for all operations.

Implement a queue using two stacks with O(1) amortized time complexity for all operations.

Implement a stack using two queues with O(1) amortized time complexity for all operations.

Find the first occurrence of a substring in a string, similar to strstr() function.

Find the intersection of two arrays and return the result as an array.

Find the intersection node of two linked lists

Invert (mirror) a binary tree by swapping left and right children

Determine if you can reach the last index of an array where each element represents the maximum jump length from that position

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

Learn the optimal O(1) in-place “copy-and-skip” to delete a node in a linked list without head/prev. Easy interview prep—see examples.

Reverse linked list in k groups (Hard): in-place pointer reversal with dummy node. Optimal O(n) time, O(1) space—step-by-step solution.

Traverse a binary tree level by level from left to right.

Find the longest common prefix string amongst an array of strings.

Find the length of the longest common subsequence between two strings

Find the length of the longest consecutive elements sequence in an unsorted array.

Find the length of the longest increasing subsequence in an array

Find the longest substring that appears at least twice in a string

Find the lowest common ancestor of two nodes in a binary tree.

Design a data structure that follows Least Recently Used (LRU) eviction with O(1) get and put operations.

Design a stack that supports push, pop, top, peekMax, and popMax operations

Find the maximum depth (height) of a binary tree

Find the maximum path sum in a binary tree.

Find the contiguous subarray with maximum sum using Kadane's algorithm

Given an array of intervals where intervals[i] = [start_i, end_i], merge all overlapping intervals and return an array of the non-overlapping intervals that cover all the intervals in the input.

Merge k sorted linked lists into one sorted linked list

Merge two sorted linked lists into one sorted linked list

Find minimum insertions needed to balance parentheses string

Find the minimum number of swaps required to sort an array.

Find the missing number in an array containing n distinct numbers taken from 0, 1, 2, ..., n.

Place n queens on an n x n chessboard such that no two queens attack each other, and return all distinct solutions

Find the next greater element for each element in an array.

Count the number of islands in a 2D grid

Check if a linked list is a palindrome using O(1) extra space

Partition a linked list around a value x such that all nodes less than x come before nodes greater than or equal to x

Check if there exists a root-to-leaf path with given sum.

Given an array of distinct integers, return all the possible permutations in any order

Traverse binary tree in postorder (left, right, root)

Check if a given integer is a power of two.

Print all root-to-leaf paths in a binary tree

Return an array where each element is the product of all elements except the element at that index.

Implement regular expression matching with '.' and '*'

Remove all duplicate values from a sorted linked list

Remove k digits from a number to make it as small as possible

Remove the nth node from the end of a linked list in one pass

Reorder a linked list by interleaving nodes from the beginning and end

Reverse the bits of a given 32-bit unsigned integer.

Learn how to reverse a singly linked list (LeetCode 206) with the optimal 3-pointer iterative method: O(n) time, O(1) space. Practice now.

Reverse a string in-place using O(1) extra memory.

Rotate a linked list to the right by k places

Given a rotated sorted array and a target value, return the index of the target if found in O(log n) time, or -1 if not present.

JSON vs Protocol Buffers vs Avro vs Thrift - choosing the right format

Find the single number that appears once in an array where every other number appears twice.

Find the maximum element in each sliding window of size k.

Sort a linked list in O(n log n) time using constant extra space

Compress a string by replacing consecutive characters with character and count.

Find all strongly connected components in a directed graph

Find a subarray with a given sum in an array of positive integers.

Given an integer array of unique elements, return all possible subsets (the power set)

Swap every two adjacent nodes in a linked list

Check if a binary tree is symmetric around its center.

Find the minimum number of intervals the CPU will take to finish all given tasks with a cooldown period between identical tasks

Find all unique triplets in the array which gives the sum of zero

Given an integer array and k, return the k most frequent elements.

Find a linear ordering of vertices in a directed acyclic graph

Find two numbers in an array that add up to a target value.

Given an array of integers and a target, return indices of two numbers that add up to the target.

Count unique paths from top-left to bottom-right in a grid

Check if a string containing only parentheses is valid.

Determine if a string can be segmented into space-separated words from a dictionary.

Solve LeetCode 140 Word Break II with DFS + memoization DP. Output-sensitive (≈O(n²)+answers). Step-by-step for interviews—practice now.

Given an m x n grid of characters and a string word, return true if the word exists in the grid by traversing adjacent cells without reusing any cell