LeetCode 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) {
if (s.equals("")) {
return true;
}

Stack<Character> stack=new Stack<>();
stack.push('s');
for (char c : s.toCharArray()) {
if (c=='(' || c=='[' || c=='{') {
stack.push(c);
}else {
if (c==')' && stack.pop()!='(') {
return false;
}
if (c==']' && stack.pop()!='[') {
return false;
}
if (c=='}' && stack.pop()!='{') {
return false;
}
}
}
if (stack.pop()!='s') {
return false;
}
return true;
}
}