摘要： Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n. For example, given n = 12, 阅读全文

摘要： For a undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible roote 阅读全文

摘要： There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third round, you toggle every 阅读全文

摘要： One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node's value. If it is a null node, 阅读全文

摘要： Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array. Formally the function should: Your algorithm 阅读全文

摘要： Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1's in their binary representation and r 阅读全文

摘要： Write a function that takes a string as input and returns the string reversed. Example:Given s = "hello", return "olleh". 代码如下： 方法一：(java) 方法二：（c++） 阅读全文

摘要： Given a positive integer n, break it into the sum of at least two positive integers and maximize the product of those integers. Return the maximum pro 阅读全文

摘要： Given a linked list, remove the nth node from the end of list and return its head. For example, 阅读全文

摘要： Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists. 代码如下: 阅读全文