20. Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

判断字符括号是否匹配正确。

java代码:

public class Solution {    public boolean isValid(String s) {        Stack a=new Stack();        int i=0;        while(i!=s.length()){            switch(s.charAt(i)){                case '[':                    a.push('[');                    break;                case '(':                    a.push('(');                    break;                case '{':                    a.push('{');                    break;                case ')':                    if(a.empty()||(char)a.pop()!='(')                    return false;                    break;                case '}':                    if(a.empty()||(char)a.pop()!='{')                    return false;                    break;                case ']':                    if(a.empty()||(char)a.pop()!='[')                    return false;                    break;            }                                        i++;        }        if(!a.empty()){            return false;        }        return true;    }}