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Given the root of a binary tree, return the bottom-up level order traversal of its nodes' values. (i.e., from left to right, level by level from leaf 阅读全文
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Given an integer n, return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n. Examp 阅读全文
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Given the root of a binary tree, return the zigzag level order traversal of its nodes' values. (i.e., from left to right, then right to left for the n 阅读全文
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Given the root of a binary tree, determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node co 阅读全文
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Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [ 阅读全文
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Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example, 2 is 阅读全文
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Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example, 2 is 阅读全文
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You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list 阅读全文
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Given an array nums of size n, return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume t 阅读全文
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Given an array of strings strs, group the anagrams together. You can return the answer in any order. An Anagram is a word or phrase formed by rearrang 阅读全文
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Given a string s, sort it in decreasing order based on the frequency of characters, and return the sorted string. Example 1: Input: s = "tree" Output: 阅读全文
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The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding one 阅读全文
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You are given two binary trees root1 and root2. Imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped w 阅读全文
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Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there ar 阅读全文
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A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null. Cons 阅读全文
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Given an integer x, return true if x is a palindrome, and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from l 阅读全文
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A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the 阅读全文
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Given the root of an n-ary tree, return the preorder traversal of its nodes' values. Nary-Tree input serialization is represented in their level order 阅读全文
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Given a n-ary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest le 阅读全文
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You are given an integer array score of size n, where score[i] is the score of the ith athlete in a competition. All the scores are guaranteed to be u 阅读全文