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“刷了300道题，面试还是被Hard题秒杀？” —— 这可能是许多LeetCode练习者的真实噩梦。当你自信满满地走进面试间，面试官却抛出一道《俄罗斯套娃信封》或《戳气球》，瞬间让你体会到什么叫"题目都看得懂，代码却无从下手"的绝望。

实不相瞒，博主在当年面试菊厂之前刷了大量Medium的题目和部分Hard的题目，面试时体感非常良好，可见平时练的难，考试就能考得好！

LeetCode 354. 俄罗斯套娃信封问题（Russian Doll Envelopes）
给定一个二维整数数组 envelopes，其中 envelopes[i] = [w_i, h_i] 表示第 i 个信封的宽度和高度。当一个信封的宽度和高度都比另一个信封大时，它可以套进去（类似俄罗斯套娃）。求最多能有多少个信封组成“套娃”序列？
⭐算法OJ⭐俄罗斯套娃信封问题【排序 + LIS】Russian Doll Envelopes

LeetCode 312. 戳气球（Burst Balloons）
给定 n 个气球，编号从 0 到 n-1，每个气球上标有一个数字 nums[i]。戳破气球 i 可以获得 nums[left] * nums[i] * nums[right] 的硬币（left 和 right 是 i 的相邻气球）。戳破后，left 和 right 变成相邻。求能获得的最大硬币数量。
⭐算法OJ⭐ 戳气球【动态规划】Burst Balloons

但别担心！这份LeetCode百大Hard题精选清单，正是破解顶级科技公司面试的"屠龙宝典"。

Why These Questions?

• 统计数据显示为高频面试考题
• 覆盖动态规划、图、树、系统设计等核心概念
• 存在复杂度$O(n)$ 或者 $O(logn)$ 的解法

分类

数组&字符串（Arrays & Strings）

• Median of Two Sorted Arrays (Binary Search)

• Trapping Rain Water (Two Pointers/Dynamic Programming)

• Longest Substring Without Repeating Characters (Sliding Window)

• Minimum Window Substring (Sliding Window + Hashmap)

• Longest Palindromic Substring (DP/Expand Around Center)

• Regular Expression Matching (DP)

• Wildcard Matching (DP)

• First Missing Positive (Array Manipulation)

• Sliding Window Maximum (Monotonic Queue)

• Find All Anagrams in a String (Sliding Window + Hash)

动态规划（Dynamic Programming / DP）

• Edit Distance (Word Transformation)

• Longest Increasing Subsequence (LIS) (Binary Search Optimized)

• Maximum Subarray (Kadane’s Algorithm)

• Coin Change (Unbounded Knapsack)

• Word Break (DP + Trie)

• Decode Ways (String to Number DP)

• Best Time to Buy and Sell Stock IV (DP with Transactions)

• Burst Balloons (Matrix Chain Multiplication DP)

• Russian Doll Envelopes (LIS Variant)

• Palindrome Partitioning II (DP Optimization)

图（Graph & BFS/DFS）

• Number of Islands (DFS/BFS)

• Course Schedule (Topological Sort)

• Alien Dictionary (Topological Sort)

• Word Ladder (BFS + Shortest Path)

• Pacific Atlantic Water Flow (Multi-Source BFS)

• Longest Consecutive Sequence (Union Find/HashSet)

• Graph Valid Tree (Union Find/DFS Cycle Detection)

• Redundant Connection (Union Find)

• Critical Connections in a Network (Tarjan’s Algorithm)

• Cheapest Flights Within K Stops (Dijkstra’s Variant)

Binary Trees & Tries

• Serialize and Deserialize Binary Tree (BFS/DFS)

• Binary Tree Maximum Path Sum (Post-Order DFS)

• Construct Binary Tree from Preorder and Inorder Traversal (Recursion)

• Word Search II (Trie + Backtracking)

• Kth Smallest Element in a BST (In-Order Traversal)

• Lowest Common Ancestor of a Binary Tree (Recursive DFS)

• Vertical Order Traversal of a Binary Tree (BFS + Sorting)

• Binary Tree Cameras (Greedy DFS)

• Sum of Distances in Tree (Post-Order + Pre-Order DFS)

• Path Sum III (Prefix Sum + DFS)

堆/优先队列（Heap & Priority Queue）

• Merge k Sorted Lists (Min-Heap)

• Find Median from Data Stream (Two Heaps)

• Top K Frequent Elements (Bucket Sort/Min-Heap)

• Task Scheduler (Greedy + Max-Heap)

• Kth Largest Element in an Array (Quickselect/Heap)

链表（Linked Lists）

• Merge Two Sorted Lists (Two Pointers)

• Reverse Nodes in k-Group (Iterative/Recursive)

• LRU Cache (Hash + Doubly Linked List)

• LFU Cache (Hash + Heaps/Linked Lists)

• Copy List with Random Pointer (Hash/Interleaving)

其他（Miscellaneous Hard Problems）

• N-Queens (Backtracking)

• Sudoku Solver (Backtracking)

• Minimum Number of Refueling Stops (Greedy + Heap)

• Race Car (BFS/DP)

• Constrained Subsequence Sum (Monotonic Queue)