JAVA学习（小白向）—栈的应用（括号匹配）—2021-06-03

JAVA学习—栈的应用（括号匹配）—2021-06-03

任务描述: 检查一个字符串的括号是否匹配. 所谓匹配, 是指每个左括号有相应的一个右括号与之对应, 且左括号不可以出现在右括号右边. 可以修改测试字符串, 检查不同情况下的运行.

1. 仅在昨天的代码基础上增加了一个 bracketMatching 方法, 以及 main 中的相应调拭语句.
2. 操作系统的核心数据结构.对于计算机而言, 如何降低时间、空间复杂度才是王道.
3. 除了关注的括号, 其它字符不起任何作用.
4. 一旦发现不匹配, 就直接返回,不用罗嗦.

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learn from @minfanphd 原文

在对元素依次进栈过程中，过程可以描述为：

遇到左括号，左括号进栈
遇到右括号，对比栈顶是否为对应的左括号
栈顶为空：输入不合法
栈顶为对应的左括号：左括号出栈
栈顶为非对应的左括号：输入不合法

代码

package a13;

/**
 * ********************
 * Char stack. Do not use Stack because it's already defined in Java.
 * @author hengyuzuo
 * ********************
 */
public class CharStack {
	/**
	 * *************
	 * The depth
	 * *************
	 */
	public static final int MAX_DEPTH = 10;
	
	/**
	 * *************
	 * The actual depth
	 * *************
	 */
	int depth;
	
	/**
	 * *************
	 * The data;
	 * *************
	 */
	char[] data;
	
	/**
	 * *************
	 * Construct an empty sequential list.
	 * *************
	 */
	public CharStack() {
		depth = 0;
		data = new char[MAX_DEPTH];
	}// Of the first constructor
	
	/**
	 * *************
	 * Overrides the method claimed in Object, the superclass of any class.
	 * *************
	 */
	public String toString() {
		String resultString = "";
		for (int i = 0; i < depth; i++) {
			resultString += data[i];
		}// Of for i 
		return resultString;
	}// Of toSting
	
	
	/**
	 * *************************
	 * Push an element.
	 * @param paraChar  the given char.
	 * @return Success or not.
	 * *************************
	 */
	public boolean push(char paraChar) {
		if (depth == MAX_DEPTH) {
			System.out.println("Stack full.");
			return false;
		}//Of if
		
		data[depth] = paraChar;
		depth++;
		return true;
	}// Of push
	
	/**
	 * *************************
	 * Pop an element.
	 * @param paraChar  the given char.
	 * @return Success or not.
	 * *************************
	 */
	public char pop() {
		if (depth == 0) {
			System.out.println("Nothin to pop.");
			return '\0';
		}// Of pop
		
		char resultChar = data[depth -1];
		depth--;
		
		return resultChar;
	}// Of pop
	
	/**
	 * **************************
	 * The entrance of the program.
	 * @param args not used now.
	 * **************************
	 */
	/*
	 * public static void main(String args[]) { CharStack tempStack = new
	 * CharStack();
	 * 
	 * for (char ch = 'a'; ch < 'm'; ch++) { tempStack.push(ch);
	 * System.out.println("The current stack is: " + tempStack); }// Of for i
	 * 
	 * char tempChar; for (int i = 0; i < 11; i++) { tempChar = tempStack.pop();
	 * System.out.println("Poped: " + tempChar);
	 * System.out.println("The current stack is: " +tempStack);} }// Of for i
	 */

		/**
		 * ************************
		 * Is the bracket matching?
		 * @param paraString the given expression.
		 * @return match or not.
		 * ************************
		 */
		public static boolean bracketMatching(String paraString) {
			//Step.1 Initialize the stack through pushing a '#' at the bottom.
			CharStack tempStack = new CharStack();
			tempStack.push('#');
			char tempChar, tempPopedChar;
			
			//Step.2 Process the string. For a string, length() is a method instead of a member variable
			for (int i =0; i < paraString.length(); i++) {
				tempChar = paraString.charAt(i);
				
				switch (tempChar) {
				case '(':
				case '[':
				case '{':
					tempStack.push(tempChar);
					break;
				case ')':
					tempPopedChar = tempStack.pop();
					if (tempPopedChar != '(') {
						return false;
					}// Of if
					break;
				case ']':
					tempPopedChar = tempStack.pop();
					if (tempPopedChar != '[') {
						return false;
					}// Of if
					break;
				default:
					// Do nothing.
				}// Of switch
			}// Of for
			
			tempPopedChar = tempStack.pop();
			if (tempPopedChar != '#') {
				return false;
			}// Of if
			
			return  true;
		}// Of bracketMatching
		
		/**
		 * *********************
		 * The entrance of the program.
		 * @param args not used now.
		 * *********************
		 */
		public static void main(String args[]) {
			CharStack tempStack = new CharStack();
			
			for (char ch = 'a'; ch < 'm'; ch++) {
				tempStack.push(ch);
				System.out.println("The current stack is: " + tempStack);
			}// Of for i 
			
			char tempChar;
			for (int i = 0; i < 11; i++) {
				tempChar = tempStack.pop();
				System.out.println("Poped: " + tempChar);
				System.out.println("The current stack is: " + tempStack);
			}// Of for i
			
			boolean tempMatch;
			String tempExpression = "[2 + (1 - 3)] * 4";
			tempMatch = bracketMatching(tempExpression);
			System.out.println("Is the expression " + tempExpression + "bracket matching?" + tempMatch);
			
			tempExpression = "( ) )";
			tempMatch = bracketMatching(tempExpression);
			System.out.println("Is the expression " + tempExpression + "bracket matching?" + tempMatch);
			
			tempExpression = "()()(())";
			tempMatch = bracketMatching(tempExpression);
			System.out.println("Is the expression " + tempExpression + "bracket matching?" + tempMatch);
			
			tempExpression = "({}[])";
			tempMatch = bracketMatching(tempExpression);
			System.out.println("Is the expression " + tempExpression + "bracket matching?" + tempMatch);
			
			tempExpression = ")(";
			tempMatch = bracketMatching(tempExpression);
			System.out.println("Is the expression " + tempExpression + "bracket matching?" + tempMatch);		
	}// Of for main1
}// Of CharStack

运行结果

The current stack is: 
Is the expression [2 + (1 - 3)] * 4bracket matching?true
Is the expression ( ) )bracket matching?false
Is the expression ()()(())bracket matching?true
Is the expression ({}[])bracket matching?false
Is the expression )(bracket matching?false

Q&A
Q1: bracketMatching是什么？

A1:所谓括号匹配，可以延伸出许多匹配问题，不限于括号。只要是两个字符就可以设置成匹配关系。常见的匹配关系：(), [], {}, ##, “”, ‘’, &&。这里就三种括号（()，[]，{}）的匹配来进行编写。