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You are a traveler on a 2D gird.

Write a function `fib(n)` that takes in a number as an argument.

Given an input string `s` and a pattern `p`, implement regular expression matching with support for `.

何处望神州？

少年不识愁滋味，爱上层楼。

呜呼！

Implement the `myAtoi(string s)` function, which converts a string to a 32-bit signed integer (similar to C/C++'s `atoi` function).

problems in Polynomial Time.

Given a string s, return the longest palindromic substring in s.