by Xiaokang Zhang | Feb 5, 2017 | Economics
经济学当中涉及到大量的数学原理，这篇文章只专注于其中关于成本和收益的一些简单概念，意在从数学的角度阐释下面的问问题： 平均总成本曲线的形状为什么是U行的？为什么边际成本曲线和平均总成本曲线总是相交于平均总成本最低点？为什么长期价格等于企业的平均总成本？为什么竞争企业的边际成本等于价格？为什么竞争市场中的企业运行在有效规模？ 概念 首先让我们厘清关于成本的若干概念：...
by Xiaokang Zhang | Jan 30, 2017 | Economics
工作之后，我们所切身关心的问题包括： 我们交了多少税？我们为什么要交这么多税？我们怎样才能少交税？ 这篇文章里，我想要重点讨论第二个问题：我们为什么要交这么多税？ 我们知道，为了维持公共机构和公共服务的运转，税收是必不可少的，“税收是我们为文明社会付出的代价”。根据社会契约的思想，每个人让渡出一部分的个人权利来组成一个政府，从而保护自己的财产等权利，税收可以视作是这让渡出的一部分权利。那么如何确定每个人应该缴纳税款的量呢？怎么样的税收制度才是有效率的？ 税收的效率...
by Xiaokang Zhang | Jan 24, 2017 | Algorithm & Data Structure
Sliding Window Sliding window is a common approach in solving algorithm problems, it has a few elements: Window start and endStatus of elements in the windowWindow extends to the right according to the statusWindow shrinks to the right according to the statusWindow...
by Xiaokang Zhang | Jan 24, 2017 | Algorithm & Data Structure
Maximum Size subarray problem Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn’t one, return 0 instead. Note:The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range....
by Xiaokang Zhang | Jan 23, 2017 | Algorithm & Data Structure
Maximum Product Subarray Problem Find the contiguous subarray within an array (containing at least one number) which has the largest product. For example, given the array [2,3,-2,4], the contiguous subarray [2,3] has the largest product = 6. Reduction Transition...