class Solution {
Stack<Character> stk = new Stack<>();
public boolean isValid(String s) {
int len=s.length();
for(int i=0;i<len;i++){
char ch = s.charAt(i);
if(stk.size()==0){
if(ch=='}'||ch==')'||ch==']') return false;//"}}}"
}
if(ch=='{'||ch=='['||ch=='('){
stk.push(ch);
}else{
if(ch==')'&&stk.peek()=='(') stk.pop();
else if(ch=='}'&&stk.peek()=='{') stk.pop();
else if(ch==']'&&stk.peek()=='[') stk.pop();
else return false;
}
}
return stk.size()==0?true:false;
}
}