a_129_ValidParenthises.java

import java.util.Stack;

public class a_129_ValidParenthises {

    public static boolean isValid(String str){
        Stack<Character> s = new Stack<>() ;

        for(int i=0; i<str.length() ; i++){   
            char ch = str.charAt(i) ;

            // opening 
            if(ch == '(' || ch == '{' || ch == '[' ) {
                s.push(ch) ;
            }
            else{    
                // closing 
                if(s.isEmpty()) {    // (((([{}]
                    return false ;
                }
                if( (s.peek() == '(' && ch == ')' ) 
                || (s.peek() == '{' && ch == '}' )
                || (s.peek() == '[' && ch == ']' ) ) {
                    s.pop() ;
                }
                else{
                    return false ;
                }

            }

        }

        if(s.isEmpty()){
            return true; 
        }
        else{
            return false; 
        }

    }
    
    public static void main(String[] args) {
        String str = "({})[()]" ;
        System.out.println( isValid(str) );  

    }
}