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Problem
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 .
Example 1:
Input: "1 + 1" Output: 2
Example 2:
Input: " 2-1 + 2 " Output: 3
Example 3:
Input: "(1+(4+5+2)-3)+(6+8)" Output: 23
Note:
You may assume that the given expression is always valid.
Do not use the eval built-in library function.
class Solution {
public int calculate(String s) {
s = s.trim().replaceAll(" ", "");
Stack stack = new Stack<>();
int sign = 1, res = 0;
System.out.println(s);
for (int i = 0; i < s.length(); i++) {
char ch = s.charAt(i);
if (ch == "+") {
sign = 1;
} else if (ch == "-") {
sign = -1;
} else if (ch == "(") {
stack.push(res);
stack.push(sign);
res = 0;
sign = 1;
} else if (ch == ")") {
res *= stack.pop();
res += stack.pop();
} else {
int sum = 0;
while (i < s.length() && Character.isDigit(s.charAt(i))) {
sum = sum*10 + (s.charAt(i)-"0");
i++;
}
res += sum*sign;
i--;
}
}
return res;
}
}
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