Basic Calculator
Implement a basic calculator to evaluate a simple expression string.
The expression string may contain open ( and closing parentheses ),
the plus + or minus sign -, non-negative integers
and empty spaces .
You may assume that the given expression is always valid.
Some examples:
"1 + 1" = 2 " 2-1 + 2 " = 3 "(1+(4+5+2)-3)+(6+8)" = 23
Note: Do not use the eval built-in
library function.
public class Solution {
public int calculate(String s) {
if (s == null || s.length() == 0)
return Integer.MAX_VALUE;
Stack<Integer> stack = new Stack<Integer>();
int number = 0;
int sign = 1;
int result = 0;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (Character.isDigit(c)) {
number = number * 10 + (int)(c - '0');
} else if (c == '+') {
result = result + number * sign;
sign = 1;
number = 0;
} else if ( c == '-') {
result = result + number * sign;
sign = -1;
number = 0;
} else if (c == '(' ){
stack.push(result);
stack.push(sign);
result = 0;
sign = 1;
} else if (c == ')') {
result = result + sign * number;
number = 0;
result = result * stack.pop();
result = result + stack.pop();
}
}
if(number != 0)
result = result + number * sign;
return result;
}
}