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BasicCalculator.java
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BasicCalculator.java
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package Leetcode;
import java.util.ArrayDeque;
import java.util.Deque;
/**
* Given a string s representing an expression, implement a basic calculator to evaluate it.
*
* Example 1:
* Input: s = "1 + 1"
* Output: 2
*
* Example 2:
* Input: s = " 2-1 + 2 "
* Output: 3
*
* Example 3:
* Input: s = "(1+(4+5+2)-3)+(6+8)"
* Output: 23
*
* Constraints:
*
* 1 <= s.length <= 3 * 105
* s consists of digits, '+', '-', '(', ')', and ' '.
* s represents a valid expression.
*/
public class BasicCalculator {
public static int calculate(String s) {
int result = 0;
int tempNum = 0;
int sign = 1;
Deque<Integer> stack = new ArrayDeque<>();
for(int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if(Character.isDigit(c)) {
tempNum = 10 * tempNum + (int)(c - '0');
} else if (c == '+') {
result += sign*tempNum;
tempNum = 0;
sign = 1;
} else if (c == '-') {
result += sign*tempNum;
tempNum = 0;
sign = -1;
} else if (c == '(') {
stack.push(result);
stack.push(sign);
// Reset the sign and value
sign = 1;
result = 0;
} else if (c == ')') {
result += sign*tempNum;
tempNum = 0;
// Accumulate the already cached result
result *= stack.pop();
result += stack.pop();
}
}
if(tempNum != 0)
result += sign*tempNum;
return result;
}
public static void main(String[] args) {
String str = "(1+(4+5+2)-3)+(6+8)";
System.out.println(calculate(str));
str = "34";
System.out.println(calculate(str));
}
}