摘要：BF的生日快到了，这一次，小东决定为BF送一份特别的生日礼物为其庆生。作为高智商中的佼佼者，BF在国外求学，因此小东无法与之一起庆生。小东计划送一个生日卡片，并通过特别的包装让BF永远难忘。她决定把卡片套装在一系列的信封A = {a1, a2, ..., an}中。小东已经从商店中购买了很多的信封， 阅读全文

摘要：Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once. Find all the elements of [1, n] 阅读全文

摘要：You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value. The path does not need t 阅读全文

摘要：Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. According to the definition of LCA on Wikipedia 阅读全文

摘要：Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. The brackets must close in the 阅读全文