# Basic Calculator

unknown
java
17 days ago
3.0 kB
4
Indexable
Never
```class Solution {
public int calculate(String s) {
return calculate(toPostfix(s));
}

private List<Node> toPostfix(String s) {
List<Node> result = new ArrayList<>();
Stack<String> stack = new Stack<>();
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (c == '*' || c == '/' || c == '-' || c == '+') {
processOperand(stack, String.valueOf(c), result);
} else if (isNumber(c)) {
i = tokens[1];
int num = tokens[0];
}
}
return result;
}

private void processOperand(Stack<String> stack, String operator, List<Node> result) {
while (!stack.isEmpty()) {
String topOperator = stack.peek();
if (getPriority(topOperator) < getPriority(operator)) {
break;
} else {
}
}
stack.push(operator);
}

private int getPriority(String operator) {
if (operator.equals("+") || operator.equals("-")) return 1;
return 2;
}

private Integer[] readNumber (String s, int start) {
int i = start;
StringBuilder sb = new StringBuilder();
while (i < s.length() && isNumber(s.charAt(i))) {
sb.append(s.charAt(i++));
}
return new Integer[] {Integer.parseInt(sb.toString()), i - 1};
}

private boolean isNumber(char c) {
return c >= '0' && c <= '9';
}

private int calculate(List<Node> list) {
Stack<Integer> stack = new Stack<>();
for (Node node : list) {
if (node.isNumber) {
stack.push(node.value);
} else if (node.operator.equals("+")) {
stack.push(stack.pop() + stack.pop());
} else if (node.operator.equals("*")) {
stack.push(stack.pop() * stack.pop());
} else if (node.operator.equals("-")) {
int second = stack.pop();
int first = stack.pop();
stack.push(first - second);
} else if (node.operator.equals("/")) {
int second = stack.pop();
int first = stack.pop();
stack.push(first / second);
}
}
return stack.pop();
}

static class Node {
boolean isNumber;
String operator;
int value;

public Node (String operator) {
this.operator = operator;
this.isNumber = false;
}

public Node (int value) {
this.value = value;
this.isNumber = true;
}
}
}```