Stacks

Stack<Integer> stack = new Stack<>();
stack.push(10);
stack.add(10);// Both add and push does the same thing
stack.pop();// return the value and pops the top
if (!stack.isEmpty());
stack.peek();// Return the top

Stacks

Stacks print in an [a, b, c] format from bottom to top

Balanced Parenthesis

Push on opener and pop on closers.

/* If the String is odd lenght, the return false*/
  Stack<Character> stack = new Stack<>();
    for (int i = 0; i < str.length(); i++) {
        char curr = str.charAt(i);

        // Push on Openers
        if (curr == '(' || curr == '[' || curr == '{') {
            stack.push(curr);
        } else { // pop on similar CLOSURES
            // ALSO CHECK IF SIMIAR IS COMING OUT
            char top = stack.peek();//top element of stack
            //System.out.println(top);
            if (    ((top == '(') && (curr == ')')) ||
                    ((top == '{') && (curr == '}')) ||
                    ((top == '[') && (curr == ']'))
                    ) {
                stack.pop();
            } else {
                return false;
            }
        }
    }
        // return (stack.empty());
        return true;

Find minimum in a Stack

Maintain 2 Stacks, One internally for keeping track of the Max/Min Stack