Question

Thus, an expression can contain a sequence of delimiters such as

            { [ ( ) ( ) ] ( ) }

but not

            [ ( ] )

For convenience, we will say that a balanced expression contains delimiters that are paired correctly, or are balanced.

1. Write a program in java that detects whether an infix expression is balance using stack structure.
2. Test your program on a set of infix algebraic expression.

Answer 1

import java.util.Stack;

public class BalancedParensChecker {

public static void main(String[] args) {

System.out.println(checkParens("(())"));

System.out.println(checkParens("[]"));

System.out.println(checkParens("(())"));

System.out.println(checkParens("{[]}"));

System.out.println(checkParens("{ [ ( ) ( ) ] ( ) }"));

System.out.println(checkParens(" [ ( ] )"));

}

private static boolean isBalanced(char ch, Stack<Character> mystack) {

boolean flag = false;

switch (ch) {

case ']':

if (!mystack.isEmpty() && (char) mystack.peek() == '[') {

mystack.pop();

flag = true;

} else {

System.out.println("Unbalanced right paranthesis were found");

System.exit(0);

}

break;

case '}':

if (!mystack.isEmpty() && (char) mystack.peek() == '{') {

mystack.pop();

flag = true;

} else {

System.out.println("Unbalanced right paranthesis were found");

System.exit(0);

}

break;

case ')':

if (!mystack.isEmpty() && (char) mystack.peek() == '(') {

mystack.pop();

flag = true;

} else {

System.out.println("Unbalanced right paranthesis were found");

System.exit(0);

}

break;

default:

flag = false;

}

return flag;

}

public static boolean checkParens(String s) {

if (s == null) {

return false;

}

boolean isBalancedParenthesis = false;

char[] arr = s.toCharArray();

Stack<Character> st = new Stack<Character>();

for (char ch : arr) {

if ((ch >= '0' && ch <= '9') || ch == '+' || ch == '-' || ch == '*' || ch == '/') {

continue;

}

if (ch == '[' || ch == '{' || ch == '(') {

st.push(ch);

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

isBalancedParenthesis = isBalanced(ch,st);

}

}

if (!st.isEmpty()) {

System.out.println("Unbalanced left paranthesis were found");

System.exit(0);

}

return isBalancedParenthesis;

}

}

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