Valid Parentheses

1. Problem

一个字符串只能包含 '(', ')', '{', '}', '[' 和 ']'，判断字符串是否是闭合有效字符串。

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.

2. Solution

用字符串数组来模拟栈

public class Solution {
    public boolean isValid( String s ){
        int len = s.length();
        if( len % 2 != 0 )
            return false;
        char[] left = new char[len];
        int count = -1;
        for( int i=0; i<len; i++ ){
            char curr = s.charAt(i);
            if( curr=='(' || curr=='{' || curr=='['  )
                left[++count] = s.charAt(i);
            else{
                if( count>=0 && ( left[count] == curr-2 || left[count] == curr-1 ) )
                    count--;
                else return false;
            }        
        }
        if( count>=0 )
            return false;
        return true;
    }
}