Difficulty: medium
Reverse Polish notation (or RPN) is a postfix notation for mathematical
expressions in which operators appear after their operands. More precisely,
the operators appear immediately after their second operand. For example the
expression 1 + 1 is written as 1 1 + in RPN and 1 - 2 + 3 becomes
1 2 - 3 +.
Implement a method that given a string holding an RPN expression computes its result.
func evaluate(_ rpnString: String) throws -> Int {
// ?
}
You can assume the string to only contain whitespace, integer numbers and the
operators +, - and *. If the string does not constitute a valid RPN
expression an error should be thrown.
To start working on this challenge open Challenge.swift and uncomment the code skeleton.
To run unit tests that validate your code, uncomment the body of the test method
in ChallengeTests.swift and hit CMD + U in Xcode. On Linux you can run the
tests by executing swift test in the package directory.
To view selected solutions open Solutions.swift.