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/**
* Evaluate a numeric operations string in postfix notation using a stack.
* Supports basic arithmetic operations: +, -, *, /
* @see https://www.geeksforgeeks.org/evaluation-of-postfix-expression/
* @param {string} expression - Numeric operations expression to evaluate. Must be a valid postfix expression.
* @returns {number|null} - Result of the expression evaluation, or null if the expression is invalid.
*/
function evaluatePostfixExpression(expression) {
const stack = []
// Helper function to perform an operation and push the result to the stack. Returns success.
function performOperation(operator) {
const rightOp = stack.pop() // Right operand is the top of the stack
const leftOp = stack.pop() // Left operand is the next item on the stack
if (leftOp === undefined || rightOp === undefined) {
return false // Invalid expression
}
switch (operator) {
case '+':
stack.push(leftOp + rightOp)
break
case '-':
stack.push(leftOp - rightOp)
break
case '*':
stack.push(leftOp * rightOp)
break
case '/':
if (rightOp === 0) {
return false
}
stack.push(leftOp / rightOp)
break
default:
return false // Unknown operator
}
return true
}
const tokens = expression.split(/\s+/)
for (const token of tokens) {
if (!isNaN(parseFloat(token))) {
// If the token is a number, push it to the stack
stack.push(parseFloat(token))
} else {
// If the token is an operator, perform the operation
if (!performOperation(token)) {
return null // Invalid expression
}
}
}
return stack.length === 1 ? stack[0] : null
}
export { evaluatePostfixExpression }