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) { char[] charArray = s.toCharArray(); Stack<Integer> stack = new Stack<>(); int res = 0; int sign = 1; stack.push(1); for (int i = 0; i < charArray.length; i++) { if (Character.isDigit(charArray[i])) { int num = charArray[i] - '0'; int j = i + 1; while (j < charArray.length && Character.isDigit(charArray[j])) { num = num * 10 + charArray[j] - '0'; j++; } res += sign * stack.peek() * num; i = j - 1; } else if (charArray[i] == '+') { sign = 1; } else if (charArray[i] == '-') { sign = -1; } else if (charArray[i] == '(') { stack.push(sign * stack.peek()); sign = 1; } else if (charArray[i] == ')') { stack.pop(); } else { ; } } return res; } }
public class Solution { public int calculate(String s) { Stack<Integer> stack = new Stack<>(); int res = 0; int sign = 1; int num = 0; for (int i = 0; i < s.length(); i++) { char ch = s.charAt(i); if (ch <= '9' && ch >= '0') { num = 10 * num + ch - '0'; } else if (ch == '+') { res += sign * num; sign = 1; num = 0; } else if (ch == '-') { res += sign * num; sign = -1; num = 0; } else if (ch == '(') { stack.push(res); stack.push(sign); res = 0; sign = 1; } else if (ch == ')') { res += sign * num; num = 0; res *= stack.pop(); res += stack.pop(); } } if (num != 0) { res += sign * num; } return res; } }