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Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the g 阅读全文
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Share Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain t 阅读全文
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Given an array of integers nums, half of the integers in nums are odd, and the other half are even. Sort the array so that whenever nums[i] is odd, i 阅读全文
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One way to serialize a binary tree is to use preorder traversal. When we encounter a non-null node, we record the node's value. If it is a null node, 阅读全文
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Given a string s, reverse the string according to the following rules: All the characters that are not English letters remain in the same position. Al 阅读全文
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Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string. Note: You mus 阅读全文
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There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edge 阅读全文
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Given an m x n board of characters and a list of strings words, return all words on the board. Each word must be constructed from letters of sequentia 阅读全文
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Given an m x n grid of characters board and a string word, return true if word exists in the grid. The word can be constructed from letters of sequent 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. 一般如果只 阅读全文