Question

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

import static java.lang.System.in;
import static java.lang.System.out;

/*
 *
 *
Use a stack to check parentheses, balanced and nesting
 *  The parentheses are: (), [] and {}
 *
 *  See:
 *  - UseAStack
 *
 */

public class Ex3CheckParen {


    public static void main(String[] args) {
        new Ex3CheckParen().program();
    }


    void program() {
        // All should be true
        out.println(checkParentheses("()"));

        out.println(checkParentheses("(()())"));

        out.println(!checkParentheses("(()))")); // Unbalanced

        out.println(!checkParentheses("((())")); // Unbalanced


        out.println(checkParentheses("({})"));

        out.println(!checkParentheses("({)}"));  // Bad nesting

        out.println(checkParentheses("({} [()] ({}))"));

        out.println(!checkParentheses("({} [() ({)})"));  // Unbalanced and bad nesting

    }


    // This is interesting because have to return, but what if no match?!?

    boolean checkParentheses(String str) {
        Deque<Character> stack = new ArrayDeque<>();

        String k = "({[";
        String s = ")]}";
        for (int i = 0; i < str.length(); i++) {
            if (k.contains(String.valueOf(str.charAt(i)))) {
                stack.push(str.charAt(i));
            } else if (s.contains(String.valueOf(str.charAt(i)))) {

                if (matching(stack.peek()) == str.charAt(i)) { //ILLEGAL ARGUMENT EXCEPTION HERE
                    return true;
                }
            } else {
                return false;
            }
        }
        return false;
    }


    char matching(char ch) {
        //char c =  must initialize but to what?!

        switch (ch) {
            case ')':
                return '('; // c = '('

            case ']':
                return '[';

            case '}':
                return '{';

            default:
                // return c;

                throw new IllegalArgumentException("No match found");
        }
    }
}

我在包含匹配的if语句中收到异常错误。无法弄清楚原因。

Answer 1

也许是这样的？

public class Ex3CheckParen {

public static void main(String[] args) {
    new Ex3CheckParen().program();
}

void program() {
    // All should be true
    out.println(checkParentheses("()"));

    out.println(checkParentheses("(()())"));

    out.println(!checkParentheses("(()))")); // Unbalanced

    out.println(!checkParentheses("((())")); // Unbalanced

    out.println(checkParentheses("({})"));

    out.println(!checkParentheses("({)}")); // Bad nesting

    out.println(checkParentheses("({} [()] ({}))"));

    out.println(!checkParentheses("({} [() ({)})")); // Unbalanced and bad nesting

}

// This is interesting because have to return, but what if no match?!?

boolean checkParentheses(String str) {
    Deque<Character> stack = new ArrayDeque<>();

    String k = "({[";
    String s = ")]}";
    for (int i = 0; i < str.length(); i++) {
        if (k.contains(String.valueOf(str.charAt(i)))) {
            stack.push(str.charAt(i));
        } else if (s.contains(String.valueOf(str.charAt(i)))) {

            if (matching(stack.peek(), str.charAt(i))) {
                return true;
            }
        } else {
            return false;
        }
    }
    return false;
}

boolean matching(char ch1, char ch2) {

    if ('(' == ch1 && ch2 == ')' || '[' == ch1 && ch2 == ']' || '{' == ch1 && ch2 == '}') {
        return true;
    }

    return false;

}

}

顺便说一下，方法checkParentheses（String str）看起来应该更像这样：

boolean checkParentheses(String str) {
    Deque<Character> stack = new ArrayDeque<>();

    String open = "({[";
    String close = ")]}";
    int length = 0;
    for (int i = 0; i < str.length(); i++) {
        char currentChar = str.charAt(i);
        if (open.contains(String.valueOf(currentChar))) {
            stack.push(currentChar);
            length++;
        } else if (close.contains(String.valueOf(currentChar))) {
            if (!stack.isEmpty() && matching(stack.peek(), currentChar)) {
                stack.pop();
                length--;
            } 
            else {
                return false;
            }

        } else {
            return false;
        }
    }

    if (length == 0)
        return true;

    return false;
}

但这完全取决于你......

Java中的非法参数异常

1 个答案: