20. 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) {
LinkedList<Character> stack = new LinkedList<Character>();
for (int i = 0; i < s.length(); i++) {
if (stack.isEmpty() || s.charAt(i) == '(' || s.charAt(i) == '{' || s.charAt(i) == '[') {
stack.push(s.charAt(i));
}
else if(s.charAt(i) == ')' && stack.peek() == '(' ){
stack.pop();
}
else if(s.charAt(i) == '}' && stack.peek() == '{' ){
stack.pop();
}
else if(s.charAt(i) == ']' && stack.peek() == '[' ){
stack.pop();
}
else{
return false;
}
}
return stack.isEmpty();
}
}