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