C#检查表达式是否有效 [英] C# checking if expression is brackets valid

问题描述

表达式:

"(a[i]+{-1}*(8-9))"

"( a[i]+{-1}*(8-9) )"

应该返回 true，因为这样编写语法是有效的.每个左括号都有一个正确的位置，并且所有括号都在合法位置.
我试图通过一个堆栈来做到这一点，我知道我错在哪里，但我想知道一种相关的方法来解决这个问题.谢谢！
我可怜可怜的错误代码:

should return true since it is valid to write syntax like this. Every left bracket has a right closer in the correct place and all brackets are at legal positions.
I tried to do this via one stack and I know where I'm wrong but I want to know a relevant way to solve this. thx!
My poor poor wrong code:

            string expression = "( a[i]+{-1}*(8-9) ) ";
        Stack<char> expStack = new Stack<char>();
        List<char> rightBracketsHolder = new List<char>();
        for (int i = 0; i < expression.Length; i++)
        {
            if (expression[i] == '{')
            {
                expStack.Push('}');
                Console.Write("}" + " ");
            }
            else if (expression[i] == '(')
            {
                expStack.Push(')');
                Console.Write(")" + " ");
            }
            else if (expression[i] == '[')
            {
                expStack.Push(']');
                Console.Write("]" + " ");
            }
        }
        Console.WriteLine();
        for (int i = 0; i < expression.Length; i++)
        {
            if (expression[i] == '}')
            {
                rightBracketsHolder.Add('}');
                Console.Write(expression[i] + " ");
            }
            else if (expression[i] == ')')
            {
                rightBracketsHolder.Add(')');
                Console.Write(expression[i] + " ");
            }
            else if (expression[i] == ']')
            {
                rightBracketsHolder.Add(']');
                Console.Write(expression[i] + " ");
            }
        }
        Console.WriteLine();
        bool stackResult = checkValidity(expStack, rightBracketsHolder);
        if (stackResult)
            Console.WriteLine("Expression is Valid.");
        else
            Console.WriteLine("
Expression is not valid.");
        Console.ReadKey();
    }

    private static bool checkValidity(Stack<char> expStack, List<char> leftBracketsHolder)
    {
        Console.WriteLine();
        int length = leftBracketsHolder.Count;
        for (int i = 0; i < length; i++)
        {
            if (expStack.Peek().ToString().Contains(leftBracketsHolder.ToString()))
            {
                leftBracketsHolder.Remove(expStack.Peek());
                expStack.Pop();

            }
        }
        if (expStack.Count == 0 && leftBracketsHolder.Count ==0)
        {
            return true;
        }
        return false;
    }
}

推荐答案

这段代码将解决你的目的-

This code will solve your purpose -

static void Main(string[] args)
    {
        bool error = false;
        var str = "( a[i]+{-1}*(8-9) )";
        Stack<char> stack = new Stack<char>();
        foreach (var item in str.ToCharArray())
        {
            if (item == '(' || item == '{' || item == '[')
            {
                stack.Push(item);
            }
            else if(item == ')' || item == '}' || item == ']')
            {
                if (stack.Peek() != GetComplementBracket(item))
                {
                    error = true;
                    break;
                }
            }
        }

        if (error)
            Console.WriteLine("Incorrect brackets");
        else
            Console.WriteLine("Brackets are fine");
        Console.ReadLine();
    }

    private static char GetComplementBracket(char item)
    {
        switch (item)
        {
            case ')':
                return '(';
            case '}':
                return '{';
            case ']':
                return '[';
            default:
                return ' ';
        }
    }

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