what am i doing wrong here?

[Randall Twede]

euler 76 and 78 are very similar. i thought it would be a piece of cake. just have to use BigInteger instead of int
76

	public String solve()
	{
		int target = 100;
		int[] ways = new int[target + 1];
		ways[0] = 1;
 
		for(int i = 1; i <= target - 1; i++)
		{
			for (int j = i; j <= target; j++)
			{
				ways[j] += ways[j - i];
			}
		}
		return Integer.toString(ways[target]);	//190569291
	}
	public String getMessage()
	{
		return "How many different ways can one hundred be written as a sum of at least two positive integers?";
	}

using BigInteger and adding one

	public String solve()
	{
		int target = 100;
		BigInteger limit = BigInteger.valueOf(target);
		BigInteger[] ways = new BigInteger[target + 1];
		ways[0] = BigInteger.ONE;
 
		for (int i = 1; i <= target; i++)
		{
			for (int j = i; j <= target; j++)
			{
				if(ways[j] == null)
				{
					ways[j] = BigInteger.ZERO;
				}
				ways[j] = ways[j].add(ways[j - i]);
				/*if(ways[j].mod(limit) == BigInteger.ZERO)
				{
					System.out.println(ways[j]);
					return Integer.toString(j);
				}*/
			}
		}
		return ways[target].toString();//190569292
	}
	
	public String getMessage()
	{
		return "Let p(n) represent the number of different ways in which n coins can be separated into piles.\n" + 
		"Find the least value of n for which p(n) is divisible by one million.";
	}

this answer is correct
78

	public String solve()
	{
		int target = 1000000;
		BigInteger limit = BigInteger.valueOf(target);
		BigInteger[] ways = new BigInteger[target + 1];
		ways[0] = BigInteger.ONE;
 
		for (int i = 1; i <= target; i++)
		{
			for (int j = i; j <= target; j++)
			{
				if(ways[j] == null)
				{
					ways[j] = BigInteger.ZERO;
				}
				ways[j] = ways[j].add(ways[j - i]);
				if(ways[j].mod(limit) == BigInteger.ZERO)
				{
					System.out.println(ways[j]);
					return Integer.toString(j);
				}
			}
		}
		return ways[target].toString();
	}
	
	public String getMessage()
	{
		return "Let p(n) represent the number of different ways in which n coins can be separated into piles.\n" + 
		"Find the least value of n for which p(n) is divisible by one million.";
	}

this returns 5997, and the System.out.println says 3000000
the correct answer is 55374
i tried changing
System.out.println(ways[j]);
to
System.out.println(ways[j].toString());
but get the same answer
i am guessing
if(ways[j].mod(limit) == BigInteger.ZERO)
is where the problem is, but not sure

[Martin Vajsar]

I'd say you've nailed it. int is a primitive type and can be compared using ==. BigInteger is an object, for which the == operator compares references. You need to use the equals method instead.

[Randall Twede]

if(ways[j].mod(limit).equals(BigInteger.ZERO))
hmmm...i thought that would fix it but i get the same answer. i tried this also
if(ways[j].remainder(limit).equals(BigInteger.ZERO))
same result

[Jayesh A Lalwani]

Can you print out the intermediate values within the loop in both implementations. You might see why it's diverging

Also, I see there is slight differrence in code

In the first version you have

 for (int i = 1; i <= target-1; i++)  

In the next 2 versions you have

 for (int i = 1; i <= target; i++)  

[Randall Twede]

that difference is correct. #76 wants all combinations of 2 numbers that equal 100(up to 99 + 1).
#78 includes the case of all coins in one stack(100)
i might try it using long, but my guess is the number will be too big