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Evaluate a formula
A spreadsheet cell holds a small arithmetic formula, and the recalculation pass turns it into a number.
- Non-negative whole numbers with + - * / between them. No brackets.
- Multiplication and division bind tighter than addition and subtraction.
- Division truncates towards zero: 7/2 is 3.
- Whitespace anywhere is ignored.
- A division by zero makes the whole formula 0.
evaluateExpression(text: string) → int
Where you start
function evaluateExpression(text: string): number {
}Worked examples
| Call | Result |
|---|---|
evaluateExpression("2+3*4") | 14 |
evaluateExpression("10-2-3") | 5 |
evaluateExpression("7/2") | 3 |
evaluateExpression("2*3+4*5") | 26 |
Hint
Carry a running total plus one pending term. On + or - you bank the pending term; on * or / you fold the new number into it.
Reference solution in TypeScript
function evaluateExpression(text: string): number {
let total = 0;
let term = 0;
let num = 0;
let op = '+';
const clean = text.replace(/\s+/g, '');
for (let i = 0; i <= clean.length; i++) {
const c = i < clean.length ? clean[i] : '#';
if (c >= '0' && c <= '9') {
num = num * 10 + (clean.charCodeAt(i) - 48);
continue;
}
if (op === '+') {
total += term;
term = num;
} else if (op === '-') {
total += term;
term = -num;
} else if (op === '*') {
term = term * num;
} else {
if (num === 0) return 0;
term = Math.trunc(term / num);
}
op = c;
num = 0;
}
return total + term;
}