使用堆棧測試平衡定界符

Question

我根據單鏈列表創建了一個通用堆棧類，並試圖使用它來檢查用戶輸入中是否有平衡的定界符。 我正在檢查以下定界符：（）{} []

堆棧碼

public class SLStack<T> {

//initializes the first node
private SLStackNode<T> head; //initializes the first node

//constructor initializes the first node as null to simulate an empty stack
public SLStack(){
    head = null;
}

//inner node class
public static class SLStackNode<T>{
    public T data;
    public SLStackNode<T> next;
}

//adds an element to the top of the stack
public void push(T value){
    SLStackNode<T> newNode = new SLStackNode<>();
    newNode.data = value;
    newNode.next = head;
    head = newNode;
}

//removes an element from the top of the stack
public T pop(){
    if (head == null){
        throw new IllegalStateException("The list is empty.");
    }
    T value = head.data;
    head = head.next;
    return value;
}

//checks the element at the top of the stack
public T top(){
    if (head == null){
        throw new IllegalStateException("The list is empty.");
    }
    T value = head.data;
    return value;
}

public boolean isEmpty(){
    return head ==  null;
}


public void printStack(SLStackNode<T> node, int depth) {
    if (node.next != null) {
        System.out.println(depth + " : " + node.data); //recurses through the stack
        //printStack(node.next);
    }
    System.out.println(depth + " : " + node.data); //recursive base case
}
}

余額測試儀代碼

public class Balanced {
public static void main(String[] args)
{
    SLStack<ExpressionScanner.Token> delimStack = new SLStack<>();
    System.out.println("Enter one expression per line.");
    System.out.println("End the program with a period on a line by itself.");
    ExpressionScanner escan = new ExpressionScanner(new Scanner(System.in));
    while (escan.hasNext()) {
        ExpressionScanner.Token token = escan.next();

        if (token.getType() == ExpressionScanner.Token.Type.OP || token.getType() == ExpressionScanner.Token.Type.VAR){
            //ignore these tokens
            continue;
        }

        if (token.getType() == ExpressionScanner.Token.Type.DELIM_OPEN){
            //push opening delimiter to the stack
            delimStack.push(token);
        }

        if (token.getType() == ExpressionScanner.Token.Type.DELIM_CLOSE){
            //look for matching opening delimiter in the stack and pop it from the stack
            if (token == delimStack.top()){
                delimStack.pop();
            }else{
                throw new IllegalStateException("Imbalanced delimiter detected.");
            }
        }

        if (delimStack.isEmpty()){
            System.out.println("Delimiters are balanced.");
        }else{
            System.out.println("Imbalanced delimiter detected.");
        }

        //System.out.println(token);
    }
}
}

當我運行測試儀時，總是說定界符是不平衡的，無論它是什么。 即使只執行一個打開的定界符，它也會表示存在不平衡，但不會引發異常。 如果單個結束定界符或多個結束定界符，它將引發異常。 如果我有兩個打開的定界符，則不會終止。

如果有人需要，我也可以發布ExpressionScanner的代碼。

Answer 1

            if (token == delimStack.top()){
            delimStack.pop();
        }else{
            throw new IllegalStateException("Imbalanced delimiter detected.");
        }

如果我正確地假設您的代碼在這里拋出異常，因為它期望一個DELIM_CLOSE類型的令牌但接收到DELIM_OPEN（假設您的輸入是'（）'）。

您應該檢查的是delimStack.pop（）= token.type.DELIM_OPEN。