Given an integer n, return the number of trailing zeroes in n!.

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.

Given a sorted integer array without duplicates, return the summary of its ranges.

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

去掉list重复的数据，目前总结的以下三种方法，分别是采用set集合来做、两层循环不用任何方法来做，以及一层循环采用contains（）方法来做，如下：

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

Given an array of n positive integers and a positive integer s, find the minimal length of a subarray of which the sum ≥ s. If there isn't one, return 0 instead...

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.