hackerrank

Answer

/*
Evaluates the prefix expression and calculates the result for the given
variable values.
@param {String} expression - the prefix expression to evaluate.
@param {Object} variables - all the variables in the expression are the keys of
this object and their corresponding values are the values the variable
should take
@returns {Number|null} the numerical result of the expression evaluated with the
given variable values. If the expression is invalid, it will return `null`.
*/
function result_expression(expression, variables) {
let expr = expression.split(" ");
let stack =[];
if(expr === ''){
return 0;
}
for(let i=0; i<expr.length; i++) {
if(!isNaN(expr[i]) && isFinite(expr[i])) {
stack.push(expr[i]);
}else {
let a = stack.pop();
let b = stack.pop();
if(expr[i] === "+") {
stack.push(parseInt(a) + parseInt(b));
} else if(expr[i] === "-") {
stack.push(parseInt(b) - parseInt(a));
} else if(expr[i] === "*") {
stack.push(parseInt(a) * parseInt(b));
} else if(expr[i] === "/") {
stack.push(parseInt(b) / parseInt(a));
} else if(expr[i] === "^") {
stack.push(Math.pow(parseInt(b), parseInt(a)));
}
}
}
if(stack.length > 1) {
return "ERROR";
}else {
return stack[0];
}
console.log(expression+"----"+JSON.stringify(variables));
}
process.stdin.resume();
process.stdin.setEncoding("ascii");
_input = "";
process.stdin.on("data", function (input) {
_input += input;
});
process.stdin.on("end", function () {
const [expression, variablesString] = _input.split('\n');
//UGLY: replaces single quotes with double quotes square brackets to convert the string to valid JSON
const variables = JSON.parse(variablesString.replace(/'/g, '"').replace(/\(/g, '[').replace(/\)/g, ']'));
console.log(result_expression(expression, variables));
});