gistfile1.pde

public class JavaTest
{
	public static void main(String[] args) throws Exception
	{
		String str = "123456789";

		// 数字をどこで区切るかのパターン総当たり
		int separatePatterns = (int)Math.pow(2, (str.length() - 1));
		for(int i=0; i<separatePatterns; i++)
		{
			String bin = paddingZeroToLeft(Integer.toString(i, 2), (str.length() - 1));
			int[] operands = splitNumber(str, toIntArray(bin));

			// + or -の演算子パターン総当たり
			int operatePatterns = (int)Math.pow(2, operands.length - 1);
			for(int j=0; j<operatePatterns; j++)
			{
				String opeBin = paddingZeroToLeft(Integer.toString(j, 2), (operands.length - 1));
				int[] operators = toIntArray(opeBin);
				int result = calc(operands, operators);

				if(result == 100)
				{
					printFormula(operands, operators);
				}
			}
		}
	}

	private static String paddingZeroToLeft(String str, int columns)
	{
		StringBuffer result = new StringBuffer(str);
		for(int i=str.length(); i<columns; i++)
		{
			result.insert(0, '0');
		}

		return result.toString();
	}

	private static int[] toIntArray(String str)
	{
		int[] result = new int[str.length()];
		for(int i=0; i<str.length(); i++)
		{
			result[i] = Integer.parseInt(str.substring(i, i+1));
		}

		return result;
	}

	// 文字列を指定された区切りパターンで区切り、数値に変換する。
	private static int[] splitNumber(String str, int[] arr)
	{
		StringBuffer slashedStr = new StringBuffer();
		for(int i=0; i<str.length(); i++)
		{
			slashedStr.append(str.charAt(i));
			if(i < arr.length && arr[i] == 1)
			{
				slashedStr.append("/");
			}
		}

		String[] splittedStrs = slashedStr.toString().split("/");
		int[] result = new int[splittedStrs.length];
		for(int i=0; i<splittedStrs.length; i++)
		{
			result[i] = Integer.parseInt(splittedStrs[i]);
		}

		return result;
	}

	private static int calc(int[] operands, int[] operators)
	{
		int result = operands[0];
		for(int i=1; i<operands.length; i++)
		{
			if(operators[i-1] == 0)
			{
				// プラス
				result = result + operands[i];
			}
			else
			{
				// マイナス
				result = result - operands[i];
			}
		}

		return result;
	}

	private static void printFormula(int[] operands, int[] operators)
	{
		StringBuffer resultStr = new StringBuffer();
		resultStr.append(Integer.toString(operands[0]));
		for(int i=1; i<operands.length; i++)
		{
			if(operators[i-1] == 0)
			{
				// プラス
				resultStr.append(" + ");
			}
			else
			{
				// マイナス
				resultStr.append(" - ");
			}
			resultStr.append(operands[i]);
		}

		int result = calc(operands, operators);
		resultStr.append(" = ");
		resultStr.append(Integer.toString(result));

		System.out.println(resultStr.toString());
	}
}