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public boolean isValid(String s) {
    char[] sa = s.toCharArray();
    Stack<Character> stk = new Stack<>();
    for(char c : sa){
        if(stk.isEmpty()){
            if(isOpener(c)){//c is (, { or  [ 
                stk.push(c);
            }else{//c is ), } or  ] 
                return false;
            }
        }else{
            if(isOpener(c)){//c is (, { or  [ 
                stk.push(c);
            }else{//c is ), } or  ] 
                char top = stk.peek();
                if(compatibleOpenClose(c, top)){
                    stk.pop();
                }else{
                    return false;
                }
            }
        }
    }
    if(stk.isEmpty()) return true;
    return false;
}
public boolean isOpener(char c){
    if(c == '{' || c == '(' || c == '[')return true;
    return false;
}
public boolean compatibleOpenClose(char c, char top){
    if(top == '(' && c == ')') return true;
    if(top == '{' && c == '}') return true;
    if(top == '[' && c == ']') return true;
    return false;
    
}