Spiderman exersize

spiderman.java

public class Spiderman {

    public int spiderman(int n) {
        // we're going to calculate these for each floor, starting from first floor:
        int waysToGetToThisFloorByJumpingTwoFloors = 0; // there's no -1 floor, so there's no way to jump two floors and get to first floor
        int waysToGetToThisFloorDirectlyFromPreviousFloor = 1; // there's one way to get from 0 to 1
        int totalWaysToGetToThisFloor = 0;

        for (int floor=1; floor <= n; floor++) {
            // total ways = sum of ways ending with a big jump (2 floors) and ways ending with a small jump (1 floor):
            totalWaysToGetToThisFloor = waysToGetToThisFloorDirectlyFromPreviousFloor + waysToGetToThisFloorByJumpingTwoFloors;
            
            // now, preparing for next floor (floor+1): 
            
            // since there were X ways to get to 'floor' from floor-1,
            // and we can jump straight from floor-1 to floor+1,
            // there are exactly X ways to get to floor+1 which end with jumping two floors:
            waysToGetToThisFloorByJumpingTwoFloors = waysToGetToThisFloorDirectlyFromPreviousFloor;

            // since there were, in total, Y ways to get to 'floor',
            // and we can jump one floor from floor to floor+1, 
            // there are Y ways to get to floor+1 which end with jumping one floor:
            waysToGetToThisFloorDirectlyFromPreviousFloor = totalWaysToGetToThisFloor;
        }
        
        // we get here after the last calculation was made for floor n,
        // so totalWaysToGetToThisFloor = total ways to get to floor n, which is what we needed
        return totalWaysToGetToThisFloor;
    }
}