Baowen Leetcode Notes

Summary of Thoughts只看偶数下标上的元素（numbers[0]、numbers[2]、numbers[4]…），判断这串数字是不是单调的。 严格递增: 返回 “increasing” 严格递减: 返回 “decreasing” 既不是递增也不是递减（含相等的情况: 返回 “none” Code（Java）1234567891011121314151617String solu

动规五部曲 dp数组以及下标含义 递归公式 dp数组如何初始化 遍历顺序 打印dp数组 🧠 Summary of Thoughts可以先考虑简单一些的情况: How many ways that we can cover a 2 * N board using one type of domino (1 * 2)? 每个i列的时候，都可以是前面i-1的后面加上一个竖条。或者是i-2的后面补充

🧠 Summary of ThoughtsKey InsightWe do NOT store the infinite set explicitly. Instead, we simulate it using: A pointer next → tracks the smallest number that has never been removed A min heap → store

🧠 Summary of ThoughtsKey Observations You don’t need to fully sort the array The problem is essentially: Find the element at index n - k (0-based sorted order) Common Approaches Sorting: Sort the

🧠 Summary of Thoughts Use the bitwise XOR (^) operation to cancel out duplicate numbers. XOR has two important properties: a ^ a = 0 → same numbers cancel out a ^ 0 = a → zero does not af

🧠 Summary of Thoughts Sort + Binary Search for the first valid threshold For each spell, count how many potions satisfy: spell * potion >= success If a potion works, then all stronger potions wi

🧠 Summary of Thoughts Binary Search Update low and high to mid + 1 or mid - 1 mid = low + (high - low) / 2 return -1 ✅ Code（Java）123456789101112131415161718192021222324252627/** * Forward declarati

🧠 Summary of Thoughts Review Foundation 1 (CSE 2321), Adjacency Matrix is a method to interpret graph. For example: isConnected[i][j]. If 1, then i and j has edge to connect. Else (0), no edge betwe

🧠 Summary of Thoughts Locate key in BST, use the property of BST below: BST property: leftNode < root < rightNode if key < root.val, then call left tree recursively if key > root.val, t

🧠 Summary of Thoughts A Binary Search Tree is an ordered Binary Tree. Binary Tree (BT)、Binary Search Tree (BST)、Heap 的核心区别: Do not utilize the properties of BST (Traverse the entire tree)This metho