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.

 

public class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < s.length(); i++) {
        	char ch = s.charAt(i);
        	if (ch=='(' || ch=='{' || ch=='[') {
        		stack.push(ch);
        	}
        	if (ch==')' && (stack.empty()||stack.pop()!='(')) {
        		return false;
        	}
        	if (ch==']' && (stack.empty()||stack.pop()!='[')) {
        		return false;
        	}
        	if (ch=='}' && (stack.empty()||stack.pop()!='{')) {
        		return false;
        	}
        }
        if (!stack.empty()) {
        	return false;
        }
        return true;
    }
}