import junit.framework.TestCase;

// Question from https://www.facebook.com/groups/javaharikrishna/permalink/2189431594515722/

public class ClimbStairsTest extends TestCase {

    private static int waysToClimbStairs(final int numberOfStairs) {
        if (numberOfStairs == 0) {
            return 1;   // There's only one way: You're already there, with zero steps!
        } else if (numberOfStairs == 1) {
            return 1;   // 1 step only
//        } else if (numberOfStairs == 2) {
//            return 2;   // 1+1 and 2
        } else {
            final int solutionAfterGoingUpOneStair = waysToClimbStairs(numberOfStairs - 1);
            final int solutionAfterGoingUpTwoStairs = waysToClimbStairs(numberOfStairs - 2);
            return solutionAfterGoingUpOneStair + solutionAfterGoingUpTwoStairs;
        }
    }

    public void test() {
        assertUniqueWaysToClimbStairs(1, 0);    // There's only one way: You're already there, with zero steps!
        assertUniqueWaysToClimbStairs(1, 1);
        assertUniqueWaysToClimbStairs(2, 2);
        assertUniqueWaysToClimbStairs(3, 3);
        assertUniqueWaysToClimbStairs(5, 4);
        assertUniqueWaysToClimbStairs(8, 5);
        assertUniqueWaysToClimbStairs(13, 6);
        assertUniqueWaysToClimbStairs(21, 7);
        assertUniqueWaysToClimbStairs(34, 8);
        assertUniqueWaysToClimbStairs(55, 9);
        assertUniqueWaysToClimbStairs(89, 10);
        // Turns out, it's the Fibonacci Sequence.
    }

    private static void assertUniqueWaysToClimbStairs(final int expectedWays, final int numberOfStairs) {
        assertEquals("for <" + numberOfStairs + "> stairs;", expectedWays, waysToClimbStairs(numberOfStairs));
    }

}