leetcode-algorithms/src/BasicCalculator.java at master · anishLearnsToCode/leetcode-algorithms · GitHub

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import java.util.Stack;

class BasicCalculator {

public int calculate(String s) {

final Stack<Integer> stack = new Stack<Integer>();

int number = 0;

int result = 0; // For the ongoing result

int sign = 1; // 1 means positive, -1 means negative

for (int i = 0; i < s.length(); i++) {

final char ch = s.charAt(i);

if (Character.isDigit(ch)) {

number = 10 * number + (ch - '0');

} else if (isOperator(ch)) {

result += sign * number;

number = 0;

sign = ch == '+' ? 1 : -1;

} else if (ch == '(') {

stack.push(result);

stack.push(sign);

sign = 1;

result = 0;

} else if (ch == ')') {

result += sign * number;

result *= stack.pop();

result += stack.pop();

number = 0;

}

return result + (sign * number);

}

private static boolean isOperator(char c) {

return c == '+' || c == '-';

}

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