Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
- Open brackets must be closed by the same type of brackets.
- Open brackets must be closed in the correct order.
Example 1:
Input: s = "()"
Output: true
Example 2:
Input: s = "()[]{}"
Output: true
Example 3:
Input: s = "(]"
Output: false
Constraints:
1 <= s.length <= 104 s consists of parentheses only '()[]{}'.
class Solution {
public boolean isValid(String s) {
if(s==null||s.length()==0){
return true;
}
Stack<Character> stack = new Stack<>();
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();
}
}