Responses for exercises in Exercism.
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#[derive(Debug)]
pub enum CalculatorInput {
Add,
Subtract,
Multiply,
Divide,
Value(i32),
}
pub fn evaluate(inputs: &[CalculatorInput]) -> Option<i32> {
let mut stack: Vec<i32> = Vec::new();
3 years ago
let last_result = inputs.iter().fold(None, |current: Option<i32>, entry| {
match (entry, stack.pop()) {
(CalculatorInput::Value(x), None) => {
stack.push(current.unwrap());
if let Some(y) = current {
stack.push(y);
}
Some(*x)
}
(CalculatorInput::Value(x), Some(y)) => {
stack.push(y);
stack.push(current.unwrap());
Some(*x)
}
(CalculatorInput::Add, Some(x)) => Some(current.unwrap() + x),
(CalculatorInput::Subtract, Some(x)) => Some(x - current.unwrap()),
(CalculatorInput::Multiply, Some(x)) => Some(x * current.unwrap()),
(CalculatorInput::Divide, Some(x)) => Some(x / current.unwrap()),
_ => None,
}
});
3 years ago
if stack.is_empty() {
last_result
} else {
// too many operands
None
}
}