“hiho” is a weekly series of contest we developed to help programmers improve their skills following some architecture. And for the beginning of this series, we present the "String". Dealing with strings is a very common problem when you go into the real world as a programmer. Although we usually use the standard methods to deal with them, these standard methods actually contain a lot of brilliant ideas inside them. So we think it's a good idea to hiho some typical string problems to all of you, as it will help hone your programming thinking.

The "longest palindrome" problem that we introduce this week, is also known as "the most popular string problem". Either in OJs, or during corporate interviews, you encounter it all the time. We collect 3 different ways to solve the problem, and show them in the order of time complexity from high to low. We believe you will gain a lot by going through these solutions. After the end of this contest, we will publish the source code of “little HO” and the list of participants who have solved this problem. Wish you learn from each other and make improvements together!