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
Go needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
func evaluateExpression(text string) int {
}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 Go
func evaluateExpression(text string) int {
clean := strings.Join(strings.Fields(text), "")
total, term, num := 0, 0, 0
op := byte('+')
for i := 0; i <= len(clean); i++ {
var c byte = '#'
if i < len(clean) {
c = clean[i]
}
if c >= '0' && c <= '9' {
num = num*10 + int(c-'0')
continue
}
switch op {
case '+':
total += term
term = num
case '-':
total += term
term = -num
case '*':
term = term * num
default:
if num == 0 {
return 0
}
term = term / num
}
op = c
num = 0
}
return total + term
}