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
C# 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
public int EvaluateExpression(string text) {
}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 C#
public int EvaluateExpression(string text) {
string clean = text.Replace(" ", "").Replace("\t", "");
int total = 0, term = 0, num = 0;
char op = '+';
for (int i = 0; i <= clean.Length; i++) {
char c = i < clean.Length ? clean[i] : '#';
if (c >= '0' && c <= '9') { num = num * 10 + (c - '0'); 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 = term / num; }
op = c;
num = 0;
}
return total + term;
}