[lintcode easy]Valid Parentheses

public class Solution {
    /**
     * @param s A string
     * @return whether the string is a valid parentheses
     */
    public boolean isValidParentheses(String s) {
        if(s==null) return false;
        if(s.length()%2 !=0) return false;
        // Write your code here
        char[] c=s.toCharArray();
        
     
        for(int i=1;i<s.length();i++)
        {
            boolean r1= c[i-1]==‘(‘ && c[i]==‘)‘;
            boolean r2= c[i-1]==‘{‘ && c[i]==‘}‘;
            boolean r3= c[i-1]==‘[‘ && c[i]==‘]‘;
            if(r1||r2||r3)
            {
                String s1=s.substring(0,i-1)+s.substring(i+1);
                if(s1.length()==0) return true;
                else return isValidParentheses(s1);
            }
        }
        return false;
    }
}