Valid Parentheses

Valid Parentheses

问题：

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.

思路：

　　经典栈的应用

我的代码：

public class Solution {

    public boolean isValid(String s) {

        if(s == null || s.length() == 0) return true;

        Stack<Character> stack = new Stack<Character>();

        for(int i = 0; i < s.length(); i++)

        {

            char c = s.charAt(i);

            if(isRight(c))

            {

                if(stack.isEmpty()) return false;

                char left = stack.pop();

                if(!isMatch(left,c)) return false;

            }

            else

            {

                stack.push(c);

            }

        }

        return stack.isEmpty();

    }

    public boolean isMatch(char left, char right)

    {

        if((left=='('&&right==')')||(left=='['&&right==']')||(left=='{'&&right=='}'))   return true;

        return false;

    }

    public boolean isRight(char c)

    {

        if(c == ')' || c == ']' || c == '}')    return true;

        return false;

    }

}

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