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GeezerVison is showing github.com — Java/DataStructures/Stacks/InfixToPostfix.java at master · JavaInCloud/Java

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InfixToPostfix.java

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package DataStructures.Stacks;
import java.util.Stack;
public class InfixToPostfix {
public static void main(String[] args) throws Exception {
assert "32+".equals(infix2PostFix("3+2"));
assert "123++".equals(infix2PostFix("1+(2+3)"));
assert "34+5*6-".equals(infix2PostFix("(3+4)*5-6"));
}
public static String infix2PostFix(String infixExpression) throws Exception {
if (!BalancedBrackets.isBalanced(infixExpression)) {
throw new Exception("invalid expression");
}
StringBuilder output = new StringBuilder();
Stack<Character> stack = new Stack<>();
for (char element : infixExpression.toCharArray()) {
if (Character.isLetterOrDigit(element)) {
output.append(element);
} else if (element == '(') {
stack.push(element);
} else if (element == ')') {
while (!stack.isEmpty() && stack.peek() != '(') {
output.append(stack.pop());
}
stack.pop();
} else {
while (!stack.isEmpty() && precedence(element) <= precedence(stack.peek())) {
output.append(stack.pop());
}
stack.push(element);
}
}
while (!stack.isEmpty()) {
output.append(stack.pop());
}
return output.toString();
}
private static int precedence(char operator) {
switch (operator) {
case '+':
case '-':
return 0;
case '*':
case '/':
return 1;
case '^':
return 2;
default:
return -1;
}
}
}
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