Description
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:
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| Input: "1 + 1"
Output: 2
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Example 2:
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| Input: " 2-1 + 2 "
Output: 3
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Example 3:
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| Input: "(1+(4+5+2)-3)+(6+8)"
Output: 23
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Note:
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| public int calculate(String s) {
s = s.replaceAll("\\s+", "");
int cal = 0, o = 1;
char[] exp = s.toCharArray();
Deque<Integer> stack = new ArrayDeque<>();
for (int i = 0; i < exp.length; i++){
switch(exp[i]){
case '(':
stack.offerFirst(cal); stack.offerFirst(o);
cal = 0; o = 1;
break;
case ')':
cal = stack.poll() * cal + stack.poll();
break;
case '+':
case '-':
o = exp[i] == '+' ? 1 : -1;
break;
default:
int num = exp[i] - '0';
while(i + 1 < exp.length && Character.isDigit(exp[i + 1]))
num = num * 10 + (exp[++i] - '0');
cal += o * num;
}
}
return cal;
}
|
