Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where:

'.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial).

Some statements in the approach directly affect some corner cases, for example, comment out line 22-23, then the unittest test_symbol_0 will fail. Hope this script helps us better understand the problem.