困难难度题单

寻找两个正序数组的中位数

Find the median of two sorted arrays using binary search for efficient O(log(min(m, n))) time complexity.

正则表达式匹配

The Regular Expression Matching problem involves checking if a string matches a pattern using '.' and '*'.

合并 K 个升序链表

Merge k Sorted Lists requires efficiently combining multiple sorted linked lists into one using pointers and priority qu…

K 个一组翻转链表

Reverse Nodes in k-Group challenges you to reverse segments of a linked list in groups of size k.

串联所有单词的子串

Find all starting indices of substrings in a string that are concatenations of a given list of words.

最长有效括号

Compute the length of the longest well-formed parentheses substring using state transition dynamic programming and stack…

解数独

Solve the Sudoku puzzle by filling empty cells while respecting Sudoku's rules using array scanning and backtracking.

缺失的第一个正数

Identify the smallest missing positive integer in an unsorted array using constant space and linear time scanning techni…

接雨水

Calculate the total trapped rain water using the elevation map array, leveraging dynamic programming and two-pointer pat…

通配符匹配

Implement full wildcard pattern matching using '?' and '*' by applying state transition dynamic programming with careful…

N 皇后

Solve the N-Queens problem using backtracking with pruning, exploring all valid board placements while avoiding conflict…

N 皇后 II

Solve the N-Queens II problem using backtracking with pruning to efficiently count all valid placements for n queens on …

排列序列

Find the kth permutation sequence of a set of numbers using math and recursion to efficiently compute the result.

有效数字

Determine if a given string represents a valid number using precise string parsing and character validation rules.

文本左右对齐

Text Justification requires packing words into lines to match a specified width, ensuring even distribution of spaces.

最小覆盖子串

Find the smallest substring of s containing all characters from t using a sliding window with running state updates for …

柱状图中最大的矩形

Find the maximal rectangular area in a histogram using stack-based state management for precise bar tracking and width c…

最大矩形

Compute the largest rectangle of 1's in a binary matrix using dynamic programming and stack-based state transitions effi…

扰乱字符串

Scramble String is a dynamic programming problem where we determine if one string can be scrambled to form another using…

不同的子序列

Compute the number of distinct subsequences of one string matching another using precise state transition dynamic progra…

买卖股票的最佳时机 III

Determine the maximum profit from at most two stock transactions using state transition dynamic programming on price arr…

二叉树中的最大路径和

Calculate the maximum sum of any path in a binary tree by exploring all node sequences using DFS and dynamic programming…

单词接龙 II

Find all shortest transformation sequences from beginWord to endWord using a dictionary, leveraging backtracking search …

单词接龙

Find the shortest transformation sequence from a start word to an end word, with each word in the sequence differing by …