如何检查字符串是否平衡?

时间:2013-02-18 05:29:34

标签: java string stack balance

我想测试输入字符串是否平衡。如果有匹配的开括号,括号或括号,它将是平衡的。

example:
{} balanced
() balanced
[] balanced
If S is balanced so is (S)
If S and T are balanced so is ST


public static boolean isBalanced(String in)
{
    Stack st = new Stack();

    for(char chr : in.toCharArray())
    {
        if(chr == '{')
            st.push(chr);

    }

    return false;
}

我在选择做什么时遇到了问题。我应该将每个开口或右括号,括号或括号放入堆叠中然后将它们弹出?如果我把它们弹出来,这对我有什么帮助呢?

8 个答案:

答案 0 :(得分:22)

1)对于每个开口括号:{ [ (将其推入堆栈。

2)对于每个结束括号:} ] )从堆栈中弹出并检查括号的类型是否匹配。如果没有返回false;

即。字符串中的当前符号为},如果来自堆栈的其他任何内容来自{,则会立即返回false

3)如果行尾和堆栈不为空,则返回false,否则true

答案 1 :(得分:9)

是的,堆栈是任务的合适选择,或者您可以使用递归函数。如果您使用堆栈,那么您的想法就是将每个开口括号推到堆栈上,当您遇到一个右括号时,您会检查堆栈的顶部是否与它匹配。如果匹配,则将其弹出,如果不匹配则为错误。完成后,堆栈应为空。

import java.util.Stack;
public class Balanced {
    public static boolean isBalanced(String in)
    {
        Stack<Character> st = new Stack<Character>();

        for(char chr : in.toCharArray())
        {
            switch(chr) {

                case '{':
                case '(':
                case '[':
                    st.push(chr);
                    break;

                case ']':
                    if(st.isEmpty() || st.pop() != '[') 
                        return false;
                    break;
                case ')':
                    if(st.isEmpty() || st.pop() != '(')
                        return false;
                    break;
                case '}':
                    if(st.isEmpty() || st.pop() != '{')
                        return false;
                    break;
            }
        }
        return st.isEmpty();
    }
    public static void main(String args[]) {
        if(args.length != 0) {
            if(isBalanced(args[0]))
                System.out.println(args[0] + " is balanced");
            else
                System.out.println(args[0] + " is not balanced");
        }
    }
}

答案 2 :(得分:2)

以下是Java代码示例,用于检测字符串是否平衡。

http://introcs.cs.princeton.edu/java/43stack/Parentheses.java.html

这个想法是 -

  • 对于每个左大括号( [ {,将其推到堆叠上。
  • 要关闭大括号) ] },请尝试从堆栈中弹出匹配的左大括号( [ }。如果找不到匹配的左括号,则字符串不平衡。
  • 如果在处理完整的字符串后,堆栈为空,则字符串是平衡的。否则字符串不平衡。

答案 3 :(得分:1)

嗯,粗略地说,如果它是平衡的,那意味着你的堆栈应该是空的。

为此,您需要在解析}

时弹出堆栈

其他要求是检查}前面是{,或者弹出的字符是{

答案 4 :(得分:1)

我编写了这段代码来解决此问题,每个括号类型仅使用一个整数(或一个字节)变量。

public boolean checkWithIntegers(String input) {

    int brackets = 0;

    for (char c: input.toCharArray()) {

        switch (c) {

            case '(':

                brackets++;

                break;

            case ')':

                if (brackets == 0)
                    return false;

                brackets--;

                break;

            default:

                break;
        }
    }


    return brackets == 0;
}

public static void main(String... args) {

    Borrar b = new Borrar();
    System.out.println( b.checkWithIntegers("") );
    System.out.println( b.checkWithIntegers("(") );
    System.out.println( b.checkWithIntegers(")") );
    System.out.println( b.checkWithIntegers(")(") );
    System.out.println( b.checkWithIntegers("()") );

}

OBS

  1. 我假设一个空字符串是平衡的。只需事先检查即可更改。
  2. 我仅使用一种类型的括号示例,但是可以添加其他大小写开关来快速添加其他类型的括号。

希望此帮助。 干杯!

答案 5 :(得分:0)

import java.util.Stack;

public class SyntaxChecker {

    /**
     * This enum represents all types of open brackets. If we have a new type then
     * just add it to this list with the corresponding closed bracket in the other
     * ClosedBracketTypes enum  
     * @author AnishBivalkar
     *
     */
    private enum OpenBracketTypes {
        LEFT_ROUND_BRACKET('('),
        LEFT_SQUARE_BRACKET('['),
        LEFT_CURLY_BRACKET('{');

        char ch;

        // Constructs the given bracket type
        OpenBracketTypes(char ch) {
            this.ch = ch;
        }

        // Getter for the type of bracket
        public final char getBracket() {
            return ch;
        }


        /**
         * This method checks if the current character is of type OpenBrackets
         * @param name
         * @return True if the current character is of type OpenBrackets, false otherwise
         */
        public static boolean contains(final char name) {
            for (OpenBracketTypes type : OpenBracketTypes.values()) {
                if (type.getBracket() == name) {
                    return true;
                }
            }

            return false;
        }
    }

    /**
     * This enum represents all types of Closed brackets. If we have a new type then
     * just add it to this list with the corresponding open bracket in the other
     * OpenBracketTypes enum    
     * @author AnishBivalkar
     *
     */
    private enum CloseBracketTypes {
        RIGHT_ROUND_BRACKET(')'),
        RIGHT_SQUARE_BRACKET(']'),
        RIGHT_CURLY_BRACKET('}');

        char ch;
        CloseBracketTypes(char ch) {
            this.ch = ch;
        }

        private char getBracket() {
            return ch;
        }

        /**
         * This method checks if a given bracket type is a closing bracket and if it correctly
         * completes the opening bracket
         * @param bracket
         * @param brackets
         * @return
         */
        public static boolean isBracketMatching(char bracket, Stack<Character> brackets) {
            // If the current stack is empty and we encountered a closing bracket then this is
            // an incorrect syntax
            if (brackets.isEmpty()) {
                return false;
            } else {
                if (bracket == CloseBracketTypes.RIGHT_ROUND_BRACKET.getBracket()) {
                    if (brackets.peek() == OpenBracketTypes.LEFT_ROUND_BRACKET.getBracket()) {
                        return true;
                    }
                } else if (bracket == CloseBracketTypes.RIGHT_SQUARE_BRACKET.ch) {
                    if (brackets.peek() == OpenBracketTypes.LEFT_SQUARE_BRACKET.getBracket()) {
                        return true;
                    }
                } else if (bracket == CloseBracketTypes.RIGHT_CURLY_BRACKET.ch) {
                    if (brackets.peek() == OpenBracketTypes.LEFT_CURLY_BRACKET.getBracket()) {
                        return true;
                    }
                }

                return false;
            }
        }

        /**
         * This method checks if the current character is of type ClosedBrackets
         * @param name
         * @return true if the current character is of type ClosedBrackets, false otherwise
         */
        public static boolean contains(final char name) {
            for (CloseBracketTypes type : CloseBracketTypes.values()) {
                if (type.getBracket() == name) {
                    return true;
                }
            }

            return false;
        }
    }


    /**
     * This method check the syntax for brackets. There should always exist a
     * corresponding closing bracket for a open bracket of same type.
     * 
     * It runs in O(N) time with O(N) worst case space complexity for the stack
     * @param sentence The string whose syntax is to be checked
     * @return         True if the syntax of the given string is correct, false otherwise
     */
    public static boolean matchBrackets(String sentence) {
        boolean bracketsMatched = true;

        // Check if sentence is null
        if (sentence == null) {
            throw new IllegalArgumentException("Input cannot be null");
        }

        // Empty string has correct syntax
        if (sentence.isEmpty()) {
            return bracketsMatched;
        } else {
            Stack<Character> brackets = new Stack<Character>();
            char[] letters = sentence.toCharArray();

            for (char letter : letters) {

                // If the letter is a type of open bracket then push it 
                // in stack else if the letter is a type of closing bracket 
                // then pop it from the stack
                if (OpenBracketTypes.contains(letter)) {
                    brackets.push(letter);
                } else if (CloseBracketTypes.contains(letter)) {
                    if (!CloseBracketTypes.isBracketMatching(letter, brackets)) {
                        return false;
                    } else {
                        brackets.pop();
                    }
                }
            }

            // If the stack is not empty then the syntax is incorrect
            if (!brackets.isEmpty()) {
                bracketsMatched = false;
            }
        }

        return bracketsMatched;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        String words = "[[][][]Anfield[[]([])[]]becons()]";
        boolean isSyntaxCorrect = SyntaxChecker.matchBrackets(words);

        if (isSyntaxCorrect) {
            System.out.println("The syntax is correct");
        } else {
            System.out.println("Incorrect syntax");
        }
    }
}

欢迎任何有关此问题的反馈意见。如果你发现错误或无用,请批评。我只是想学习。

答案 6 :(得分:0)

import java.util.*;
public class Parenthesis
{
    public static void main (String ...argd)
    {
        Scanner sc=new Scanner(System.in);
        System.out.println("enetr string");
        String s=sc.nextLine();
        Stack<Character> st=new Stack<Character>();  
        for (int i=0;i<s.length();++i)
        {
            if((s.charAt(i)=='(')||(s.charAt(i)=='{')||(s.charAt(i)=='['))
            {
                st.push(s.charAt(i));
            }
            else if(st.isEmpty()==false)
            {   
            switch(s.charAt(i))
            {
            case']':
                if(st.pop()!='[')
                {
                    System.out.println("unbalanced");
                    System.exit(0);
                }
                break;
            case'}':
                if(st.pop()!='{')
                {
                    System.out.println("unbalanced");
                    System.exit(0);
                }
                break;
            case')':
                if(st.pop()!='(')
                {
                    System.out.println("unbalanced");
                    System.exit(0);
                }
                break;
            }
            }
        }           
        if(st.isEmpty())
        {
            System.out.println("balanced paranthesis");
        }
        else 
            System.out.println("not balance");
    }   
}

答案 7 :(得分:0)

对应的Hackrrank链接:https://www.hackerrank.com/challenges/balanced-brackets/problem

import java.util.Stack;

class BalancedParenthesis {
    static String isBalanced(String s) {
        return isBalanced(s.toCharArray());
    }

    private static String isBalanced(final char[] chars) {
        final Stack<Character> stack = new Stack<>();
        for (char eachChar : chars) {
            if (eachChar == '{' || eachChar == '[' || eachChar == '(') {
                stack.push(eachChar);
            } else {
                if (stack.isEmpty()) {
                    return "NO";
                }
                if (correspondingCloseBracket(stack.peek()) != eachChar) {
                    return "NO";
                }
                stack.pop();
            }
        }
        return stack.isEmpty() ? "YES" : "NO";
    }

    private static char correspondingCloseBracket(final char eachChar) {
        if (eachChar == '{') {
            return '}';
        }
        if (eachChar == '[') {
            return ']';
        }
        return ')';
    }
}