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Given an integer n, return all the structurally unique BST's (binary search trees), which has exactly n nodes of unique values from 1 to n. Return the 阅读全文
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Given an array of integers preorder, which represents the preorder traversal of a BST (i.e., binary search tree), construct the tree and return its ro 阅读全文
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Given the root of a complete binary tree, return the number of the nodes in the tree. According to Wikipedia, every level, except possibly the last, i 阅读全文
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You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day, you may decide to buy and/or sell the 阅读全文
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You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day 阅读全文
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You are given an m x n integer matrix grid where each cell is either 0 (empty) or 1 (obstacle). You can move up, down, left, or right from and to an e 阅读全文
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A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are va 阅读全文
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The Hamming distance between two integers is the number of positions at which the corresponding bits are different. Given two integers x and y, return 阅读全文