括号验证

题目大意

　　给定一个只包含(‘, ‘)’, ‘{‘, ‘}’, ‘[’ 和‘]’的字符串，验证它是不是有效的。括号必须配对，而且要以正确的顺序。

解题思路

　　用一个栈来对输入的括号串进行处理，若是是左括号就入栈，若是是右括号就与栈顶元素看是否组成一对括号，组成就弹出，而且处理下一个输入的括号，若是不匹配就直接返回结果。

代码实现

import java.util.*;

public class Solution {
    public boolean isValid(String s) {

        Deque<Character> stack = new LinkedList<>();
        int index = 0;
        Character top;
        while (index < s.length()) {
            Character c = s.charAt(index);
            switch (c) {
                case '(':
                case '[':
                case '{':
                    stack.addFirst(c);
                    break;
                case ')':

                    if (stack.isEmpty()) {
                        return false;
                    }

                    top = stack.getFirst();
                    if (top == '(') {
                        stack.removeFirst();
                    } else if (top == '[' || top == '{') {
                        return false;
                    } else {
                        stack.addFirst(c);
                    }
                    break;
                case ']':

                    if (stack.isEmpty()) {
                        return false;
                    }

                    top = stack.getFirst();
                    if (top == '[') {
                        stack.removeFirst();
                    } else if (top == '(' || top == '{') {
                        return false;
                    } else {
                        stack.addFirst(c);
                    }
                    break;
                case '}':

                    if (stack.isEmpty()) {
                        return false;
                    }

                    top = stack.getFirst();
                    if (top == '{') {
                        stack.removeFirst();
                    } else if (top == '[' || top == '(') {
                        return false;
                    } else {
                        stack.addFirst(c);
                    }
                    break;
                default:
                    return false;
            }

            index++;
        }

        return stack.isEmpty();
    }
}

 

java实现的判断括号是否成对的代码，()[]{}均可以

原本想找找现成的，去，都写的好复杂。本身写一个吧。挺有成就感。哈哈

package com.test.jiexi;   import java.util.Stack;   public class Check {       /**      * @param args      */     public static void main(String[] args) {         // TODO Auto-generated method stub         String  s="(1){CHI[与|和] || CAT[J] LOGIC[G|D]}+(2){CAT[A] || OF_AMBI[A]}+(3){CHI[的]||CAT[N]}";         Stack<Character> sc=new Stack<Character>();         char[] c=s.toCharArray();         for (int i = 0; i < c.length; i++) {             if (c[i]=='('||c[i]=='['||c[i]=='{') {                 sc.push(c[i]);             }             else if (c[i]==')') {                 if (sc.peek()=='(') {                     sc.pop();                 }             }else if (c[i]==']') {                 if (sc.peek()=='[') {                     sc.pop();                 }             }else if (c[i]=='}') {                 if (sc.peek()=='{') {                     sc.pop();                 }             }         }         if (sc.empty()) {             System.out.println("成对");         }else {             System.out.println("不成对");         }     } }