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BasicCalculator.java
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BasicCalculator.java
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public class Solution {
public int calculate(String s) {
Stack<Integer> stack = new Stack<Integer>();
int lastOp = 1;
stack.push(lastOp);
int result = 0;
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == ' ') {
continue;
} else if (s.charAt(i) == '+') {
lastOp = 1;
} else if (s.charAt(i) == '-') {
lastOp = -1;
} else if (s.charAt(i) == '(') {
stack.push(lastOp * stack.peek());
lastOp = 1;
} else if (s.charAt(i) == ')') {
stack.pop();
} else {
int k = i;
int currNumber = 0;
while (k < s.length() && Character.isDigit(s.charAt(k))) {
currNumber = currNumber * 10 + (int)s.charAt(k) - (int)'0';
k += 1;
}
i = k - 1;
result += currNumber * stack.peek() * lastOp;
}
}
return result;
}
}