问题链接

• Valid Parentheses | LeetCode OJ

问题描述

判断给出的字符串中的括号是否合法。

解决办法

public class Solution {
    public boolean isValid(String s) {
        List<String> parenthesisList = new ArrayList();
        for(int i = 0;i < s.length();i ++){
            char c = s.charAt(i);
            if(isLeftParenthesis(c)){
                parenthesisList.add(String.valueOf(c));
            }
            else if(isRightParenthesis(c)){
                if(parenthesisList.size()==0){
                    return false;
                }
                int lastPosition = parenthesisList.size() - 1;
                String lastParenthesis = parenthesisList.get(lastPosition);
                if(!isParenthesesMatch(lastParenthesis.charAt(0),c)){
                   return false;
                }
                parenthesisList.remove(lastPosition);
            }
        }
        return parenthesisList.size() == 0;
    }
    
    public static boolean isParenthesesMatch(char left,char right){
        if(left == '{' && right == '}'){
            return true;
        }
        if(left == '(' && right == ')'){
            return true;
        }
        if(left == '[' && right == ']'){
            return true;
        }
        return false;
    }
    
    public static boolean isLeftParenthesis(char c){
        switch(c){
            case '{':
            case '(':
            case '[':
                return true;
            default:
                return false;
        }
    }
    
    public static boolean isRightParenthesis(char c){
        switch(c){
            case '}':
            case ')':
            case ']':
                return true;
            default:
                return false;
        }
    }
    
    public static boolean isParenthesis(char c){
        return isLeftParenthesis(c) || isRightParenthesis(c);
    }
}