This function checks whether a given string containing only '(', ')' and '*' characters is valid. A string is considered valid if it follows the rules defined above.

Given a stack of integers, the function returns the sum of the elements in the stack.

This function takes in a string consisting only of parentheses and outputs whether or not the string is balanced. A string is balanced if every open parenthesis has a corresponding close parenthesis and there are no unmatched parentheses.

This problem asks the programmer to return the sum of all integers at even indices in a given list. For example, given the list [1, 2, 3, 4, 5], the output would be 6 (2 + 4).

Given a simple expression string consisting of parentheses, plus/minus signs, and non-negative integers, implement a basic calculator to evaluate the string.

The function should return true if the stack is in sorted order (increasing order), and false otherwise.

This problem asks you to reverse a string using a stack. An example input and output is provided.

A stack is a data structure that supports push, pop, and min operations in constant time.