When list is converted to Big Integer it throws NullPointerExceptions?

Question

I'm creating some code for a google challenge and I need to write the following function: Say you have a board game x places long, and you have a three sided dye with 'stay', 'right', 'and left'. I need to right a function that when given the amount of dice rolls and number of places and the board will return how many different ways you can get there in the correct amount of dice rolls. (Without going off the edge of the bored of course) Then Moodulas 123454321. (Don't ask me why I mod the answer to 123454321, I don't know). I have whipped up the following code, but it throws a null-pointer exception. I originally did it with plain integer lists. But they were to small and could not pass all tests. Can anyone help? Here is the code:

public static void main(String args[]) {
        System.out.print(answer(100, 10));
    }



public static int answer(int diceRolls, int numOfSquares) {

        //Two many squares to be possible. Return 0 for 0 solutions.
        if ((numOfSquares - diceRolls) > 1) {
            return 0;
        }
        //If there are only two squares there is only One option. Roll a Right.
        if (numOfSquares == 2) {
            return diceRolls;
        }
        //If there are exactly as may dice rolls as there is squares. 
        //There are as much possibilities as there are squares
        //Therefore return number of squares.
        if (diceRolls == numOfSquares) {
            return numOfSquares;
        }

        //Tests how many options there are to roll and get as many dice rolls as needed. 
        //While still getting the amount of squares needed to finish the board game.
        BigInteger listOne[] = new BigInteger[numOfSquares]; //listOnes[current] holds the number valid paths to position 'current' using 'subCurrent-1' steps
        BigInteger listTwo[] = new BigInteger[numOfSquares]; //put number of valid paths to position 'current' using 'subCurrent' steps into listTwo[current]
        BigInteger total = new BigInteger("0");
        listOne[0] = BigInteger.valueOf(1);
        listOne[1] = BigInteger.valueOf(1);
        int max = 1;

        for (int index = 1; index < diceRolls; index++) {
            listTwo = new BigInteger[numOfSquares]; //Resets listTwo
            //Adds one to max until max is correctly fitted with number of squares
            if (max < (numOfSquares - 1)) {
                max++;
            }

            for (int subIndex = 0; subIndex < numOfSquares && subIndex < (max + 1); subIndex++) {
                //If at first square
                if (subIndex == 0) {
                    //Set listTwo's current value to lstOnes current value + the next value.
                listTwo[subIndex] = listOne[subIndex].add(listOne[subIndex + 1]);
                } else if (subIndex == max) {
                    //If at final square
                    if (subIndex == (numOfSquares - 1)) {
                        total.add(listOne[subIndex - 1]); //Adds listOnes last value to total.
                    } else {
                         listTwo[subIndex] = listOne[subIndex - 1];
                    } else {
                        //If subIndex is not yet at final or first Square
                        //Set current value of listTwo to listOne's last square + current square + nextSquare
                        listTwo[subIndex] = listOne[subInde add(listOne[subIndex].add(listOne[subIndex + 1]));
                    }
                }
                listOne = listTwo; //Sets listOne to the new value of listTwo
            }

            int answer = total.mod(BigInteger.valueOf(123454321)).intValue(); //For some reason question asks to return modulo 123454321 of the number
            return answer;
        }

Now here is the stack trace:

Exception in thread "main" java.lang.NullPointerException
    at java.math.BigInteger.add(Unknown Source)
    at arrays.MinionsBoredGames.answer(MinionsBoredGames.java:59)
    at arrays.MinionsBoredGames.main(MinionsBoredGames.java:8)

Always include the stack trace and point out which line it's referring to. — chrylis -cautiouslyoptimistic-, Nov 21 '15 at 13:32
The code needs correction, it doesn't compile: listTwo[subIndex] = listOne[subInde add(listOne[subIndex].add(listOne[subIndex + 1])); — Jeff Morin, Nov 21 '15 at 13:39
But what is the correction it needs. I figured out the null exceptions is thrown at the value of `listOne[subIndex + 1]`, But why is that wrong, and how can I fix it? — Elgin Beloy, Nov 21 '15 at 13:41
Ok This might occurred because you haven't initialised the BigInteger.. — Devavrata, Nov 21 '15 at 13:45
where do you assign the value of listOne[subIndex+1] to a BigInteger? — matt, Nov 21 '15 at 13:46
Since you said you get that NullPointerException so you code can be compiled on your machine, but the code here can't. You have two `else` blocks in the nested loop and `subInde add` also looks wrong. — Tom, Nov 21 '15 at 13:47
@Devavrata Do you mean I have to initialize every element in the list — Elgin Beloy, Nov 21 '15 at 13:52
nit: use `BigInteger.ZERO` (/`ONE`). "Never" use a (`BigInteger`) constructor for constants. — greybeard, Nov 21 '15 at 13:55

When list is converted to Big Integer it throws NullPointerExceptions?

0 Answers0