Cacher is the code snippet organizer for pro developers

/**
 * 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.
 */
 
public class Solution {
    public boolean isValid(String s) {
        Stack<Character> stk = new Stack<Character>();
        if(s == null || s.length() == 0)
            return true;
        for(int i = 0; i < s.length(); i++){
            if(s.charAt(i) == ')'){
                if(!stk.isEmpty() && stk.peek() == '(')
                    stk.pop();
                else
                    return false;
            }else if(s.charAt(i) == ']'){
                if(!stk.isEmpty() && stk.peek() == '[')
                    stk.pop();
                else
                    return false;
            }else if(s.charAt(i) == '}'){
                if(!stk.isEmpty() && stk.peek() == '{')
                    stk.pop();
                else
                    return false;
            }else{
                stk.push(s.charAt(i));
            }
        }
        if(stk.isEmpty())
            return true;
        else
            return false;
    }
    
    public boolean isValid(String s) {
    	Stack<Character> stack = new Stack<Character>();
    	for (char c : s.toCharArray()) {
    		if (c == '(')
    			stack.push(')');
    		else if (c == '{')
    			stack.push('}');
    		else if (c == '[')
    			stack.push(']');
    		else if (stack.isEmpty() || stack.pop() != c)
    			return false;
    	}
    	return stack.isEmpty();
    }
}