Given an array of number find the next greater no in the right of each element.

README.md

Given an array of number find the next greater no in the right of each element.

Example-

Input 12 15 22 09 07 02 18 23 27
Output 15 22 27 18 18 18 23 27 -1

FindNextGreatestGivenArray.java

import java.util.Stack;

public class FindNextGreatestGivenArray {

    // works in O(n*n)
    public int[] findNextGreatestNumbers(int[] numbers) {

        if (numbers == null) {
            throw new IllegalArgumentException("Given array is null");
        }

        int[] output = new int[numbers.length];
        for (int i = 0; i < output.length; i++) {
            output[i] = -1;
        }

        for (int i = 0; i < output.length; i++) {

            for (int j = i + 1; j < output.length; j++) {

                if (numbers[j] > numbers[i]) {
                    output[i] = numbers[j];
                    break;
                }
            }
        }

        return output;
    }

    // works in O(n) with using stack
    public void printNextLarger(int numbers[]) {
        if (numbers.length <= 0)
            return;

        Stack<Integer> stack = new Stack<>();
        stack.push(numbers[0]);

        for (int i = 1; i < numbers.length; i++) {

            int currentElement = numbers[i];
            while (!stack.isEmpty()) {

                int leftElement = stack.pop();
                if (leftElement < currentElement) {

                    System.out.println(leftElement + " Next Largerst --> " + currentElement);
                } else {

                    stack.push(leftElement);
                    break;
                }
            }

            stack.push(currentElement);
        }

        while (!stack.isEmpty()) {

            int leftOverElement = stack.pop();
            System.out.println(leftOverElement + " Next Largerst --> None");
        }
    }
}

FindNextGreatestGivenArrayTest.java

import static org.junit.Assert.assertArrayEquals;

import org.junit.Before;
import org.junit.Test;

public class FindNextGreatestGivenArrayTest {

    private FindNextGreatestGivenArray testClass;

    @Before
    public void setUp() {

        testClass = new FindNextGreatestGivenArray();
    }

    @Test
    public void testGivenArray() {

        int[] numbers = { 12, 15, 22, 9, 7, 2, 18, 23, 27 };
        int[] expected = { 15, 22, 23, 18, 18, 18, 23, 27, -1 };
        assertArrayEquals(expected, testClass.findNextGreatestNumbers(numbers));
    }

    @Test
    public void testName() throws Exception {

        int[] numbers = { 40, 50, 11, 32, 55, 68, 75 };
        testClass.printNextLarger(numbers);
    }
}