中等难度题单

两数相加

Add Two Numbers requires careful linked-list pointer manipulation to sum digits while handling carries efficiently in in…

无重复字符的最长子串

Find the length of the longest substring without repeating characters using a sliding window and hash map to track state…

最长回文子串

Find the longest contiguous palindromic substring in a given string using dynamic programming and two-pointer expansion …

Z 字形变换

Convert a string into a zigzag pattern across multiple rows and read it line by line efficiently for string manipulation…

整数反转

Reverse Integer challenges you to invert the digits of a signed 32-bit integer, handling overflow and negative values ca…

字符串转换整数 (atoi)

Convert a string to a 32-bit signed integer by carefully parsing characters, handling signs, and ignoring invalid traili…

盛最多水的容器

Find two vertical lines that can form a container with the most water in a given array of heights.

整数转罗马数字

Convert a given integer to its Roman numeral representation using hash table mapping and decimal place math operations e…

三数之和

Given an integer array, return all unique triplets where the sum is zero using two-pointer scanning with careful duplica…

最接近的三数之和

Find the sum of three integers in an array that is closest to a given target using two-pointer scanning.

电话号码的字母组合

Generate all letter combinations a digit string can represent using backtracking with pruning, leveraging hash table map…

四数之和

The 4Sum problem requires finding all unique quadruplets in an array that sum to a specific target value.

删除链表的倒数第 N 个结点

Remove the nth node from the end of a linked list using a two-pointer approach to solve efficiently.

括号生成

Generate Parentheses requires generating all valid combinations of parentheses with given pairs using backtracking and s…

两两交换链表中的节点

Learn how to swap every adjacent linked-list pair by rewiring nodes safely without changing values or breaking the remai…

两数相除

Solve Divide Two Integers by turning repeated subtraction into bit-shifted chunk subtraction with careful sign and overf…

下一个排列

Next Permutation is a medium-difficulty problem focusing on generating the next lexicographically greater permutation of…

搜索旋转排序数组

Find the index of a target in a rotated sorted array using a careful binary search that handles pivot shifts.

在排序数组中查找元素的第一个和最后一个位置

Locate the first and last index of a target in a sorted array using binary search for precise O(log n) performance.

有效的数独

Check if a 9x9 Sudoku board is valid by scanning rows, columns, and sub-boxes with hash lookups, ensuring no duplicates …

外观数列

Count and Say requires building the nth sequence term by iteratively applying a run-length encoding on strings of digits…

组合总和

Find all unique combinations of numbers from a distinct array that sum to a target using controlled backtracking search.

组合总和 II

Find all unique combinations of numbers that sum to a target using backtracking with careful pruning to avoid duplicates…

字符串相乘

Multiply Strings requires simulating integer multiplication using only string operations without direct numeric conversi…