Function $1$: postfixEval $(14$ test cases, total $32$ points$)$

Write a function named postfixEval such that given a postfix expression, evaluate it and return the result. Assumptions:

the operands are floats

the possible operators are $+,-,**,1$

the input expression is always a valid and none$-$empty postfix expression

Example: When input is $["2","4","7","*","-"],$ which is $2-4**7$ using infix notation, your function should $-26.$

Function $2$: validParentheses $(29$ test cases, total $35$ points$)$

Given a $($possibly empty$)$ string containing only alphabet letters and parentheses $"(",")","\{","\}","[","]",$ determine if the string is valid.

$1$