简单难度题单

两数之和

Two Sum is solved fastest by storing seen values in a hash map and checking each number's needed complement once.

回文数

Determine if a given integer reads the same forward and backward using a math-driven solution strategy without convertin…

罗马数字转整数

Convert a Roman numeral string into an integer using a hash table and mathematical principles to determine value order.

最长公共前缀

Find the longest common prefix in an array of strings, returning an empty string if none exists.

有效的括号

Determine if a string of parentheses, brackets, and braces is correctly nested using a stack for proper order validation…

合并两个有序链表

Merge two sorted linked lists by splicing nodes into one sorted list using linked-list pointer manipulation and recursio…

删除有序数组中的重复项

Learn how to remove duplicates from a sorted array in-place using two-pointer scanning while preserving element order.

移除元素

Remove Element challenges you to remove a value from an array in-place using efficient two-pointer scanning and tracking…

找出字符串中第一个匹配项的下标

Locate the first occurrence of a substring within a string using a two-pointer scanning strategy and invariant tracking …

搜索插入位置

Find the correct index for a target value in a sorted array using binary search, or return the position where it should …

最后一个单词的长度

Determine the length of the last word in a string using a focused string-driven approach to handle spaces and trailing c…

加一

Given a number as an array of digits, increment it by one and return the updated array of digits.

二进制求和

Add Binary involves summing two binary strings and returning the result as a binary string using math and string manipul…

x 的平方根

Solve the Sqrt(x) problem using binary search to find the integer square root of a number without built-in operators.

爬楼梯

Climbing Stairs is a classic dynamic programming problem where you calculate distinct ways to reach the top using step t…

删除排序链表中的重复元素

Efficiently remove duplicates from a sorted linked list using precise pointer manipulation while maintaining node order …

合并两个有序数组

Merge two sorted arrays into the first array in non-decreasing order, using a two-pointer approach.

二叉树的中序遍历

Binary Tree Inorder Traversal asks you to visit left subtree, node, then right subtree without losing position while mov…

相同的树

Check whether two binary trees are identical by comparing structure and node values using DFS or BFS traversal strategie…

对称二叉树

Determine if a binary tree is symmetric by comparing left and right subtrees using DFS or BFS traversal techniques effic…

二叉树的最大深度

Find the maximum depth of a binary tree using traversal techniques to track the longest path from root to leaf.

将有序数组转换为二叉搜索树

Pick the middle element as root at each step so the sorted array becomes a height-balanced BST with valid ordering.

平衡二叉树

Determine if a binary tree is height-balanced using tree traversal and state tracking techniques.

二叉树的最小深度

Find the minimum depth of a binary tree, which is the shortest path from the root node to the nearest leaf node.