Ejerciciso pre solemne 1

BalancedParentheses.java

import java.util.*;

public class BalancedParentheses {

    public static boolean isBalanced(String expression) {
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < expression.length(); i++) {
            char c = expression.charAt(i);
            if (c == '(' || c == '{' || c == '[') {
                stack.push(c);
            } else if (c == ')' || c == '}' || c == ']') {
                if (stack.isEmpty()) {
                    return false;
                }
                char last = stack.peek();
                if ((c == ')' && last == '(') ||
                    (c == '}' && last == '{') ||
                    (c == ']' && last == '[')) {
                    stack.pop();
                } else {
                    return false;
                }
            }
        }
        if (stack.isEmpty()) return true;
        else return false;

        return stack.isEmpty();
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter an expression: ");
        String expression = scanner.nextLine();
        boolean balanced = isBalanced(expression);
        if (balanced) {
            System.out.println("The expression is balanced");
        } else {
            System.out.println("The expression is not balanced");
        }
    }
}

nextGreater.java

import java.util.*;

public class nextGreater {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        List<Integer> nums = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            nums.add(sc.nextInt());
        }
        List<Integer> result = nextGreater(nums);
        System.out.println(result); // Output: [5, 5, 9, -1, 8, -1]
    }

    public static List<Integer> nextGreater(List<Integer> nums) {
        List<Integer> result = new ArrayList<>(nums.size());
        Stack<Integer> stack = new Stack<>();
        for (int i = nums.size() - 1; i >= 0; i--) {
            while (!stack.isEmpty() && 
                   stack.peek() <= nums.get(i)) {
                stack.pop();
            }
            result.add(stack.isEmpty() ? -1 : stack.peek());
            stack.push(nums.get(i));
        }
        Collections.reverse(result);
        return result;
    }
}