private void GetMatchPoints(SubArray A, SubArray B, ArrayList MatchPoints)
{
if (A.Length > 0 && B.Length > 0)
{
//Find the middle snake from (x,y) to (u,v)
int x, u, k;
int D = FindMiddleSnake(A, B, out x, out u, out k);
int y = x - k;
int v = u - k;
if (D > 1)
{
GetMatchPoints(new SubArray(A, 1, x), new SubArray(B, 1, y), MatchPoints);
for (int i = x + 1; i <= u; i++)
{
//Output absolute X and Y (not relative to the current subarray)
MatchPoints.Add(new Point(i + A.Offset, i - k + B.Offset));
}
GetMatchPoints(new SubArray(A, u + 1, A.Length - u), new SubArray(B, v + 1, B.Length - v), MatchPoints);
}
else
{
//If there are no differences, we have to output all of the points.
//If there's only one difference, we have to output all of the
//match points, skipping the single point that is different.
Debug.Assert(D == 0 || Math.Abs(A.Length - B.Length) == 1, "A and B's lengths must differ by 1 if D == 1");
//Only go to the minimum of the two lengths since that's the
//most that can possibly match between the two subsequences.
int N = A.Length;
int M = B.Length;
if (M > N)
{
//Output A[1..N] as match points
int iCurrY = 1;
for (int i = 1; i <= N; i++)
{
//We must skip the one difference when we hit it
if (A[i] != B[iCurrY])
{
iCurrY++;
}
MatchPoints.Add(new Point(i + A.Offset, iCurrY + B.Offset));
iCurrY++;
}
}
else
{
//Output B[1..M] as match points
int iCurrX = 1;
for (int i = 1; i <= M; i++)
{
//We must skip the one difference when we hit it
if (A[iCurrX] != B[i])
{
iCurrX++;
}
MatchPoints.Add(new Point(iCurrX + A.Offset, i + B.Offset));
iCurrX++;
}
}
}
}
}
private int FindMiddleSnake(SubArray A, SubArray B, out int iPathStartX, out int iPathEndX, out int iPathK)
{
//We don't have to check the result of this because the calling procedure
//has already check the length preconditions.
SetupFictitiousPoints(A, B);
iPathStartX = -1;
iPathEndX = -1;
iPathK = 0;
int iDelta = A.Length - B.Length;
int iCeiling = (int)Math.Ceiling((A.Length + B.Length) / 2.0);
for (int D = 0; D <= iCeiling; D++)
{
for (int k = -D; k <= D; k += 2)
{
//Find the end of the furthest reaching forward D-path in diagonal k.
GetForwardDPaths(A, B, D, k);
//If iDelta is odd (i.e. remainder == 1 or -1) and ...
if ((iDelta % 2 != 0) && (k >= (iDelta - (D - 1)) && k <= (iDelta + (D - 1))))
{
//If the path overlaps the furthest reaching reverse (D-1)-path in diagonal k.
if (m_vecForward[k] >= m_vecReverse[k])
{
//The last snake of the forward path is the middle snake.
iPathK = k;
iPathEndX = m_vecForward[k];
iPathStartX = iPathEndX;
int iPathStartY = iPathStartX - iPathK;
while (iPathStartX > 0 && iPathStartY > 0 && A[iPathStartX] == B[iPathStartY])
{
iPathStartX--;
iPathStartY--;
}
//Length of an SES is 2D-1.
return(2 * D - 1);
}
}
}
for (int k = -D; k <= D; k += 2)
{
//Find the end of the furthest reaching reverse D=path in diagonal k+iDelta
GetReverseDPaths(A, B, D, k, iDelta);
//If iDelta is even and ...
if ((iDelta % 2 == 0) && ((k + iDelta) >= -D && (k + iDelta) <= D))
{
//If the path overlaps the furthest reaching forward D-path in diagonal k+iDelta.
if (m_vecReverse[k + iDelta] <= m_vecForward[k + iDelta])
{
//The last snake of the reverse path is the middle snake.
iPathK = k + iDelta;
iPathStartX = m_vecReverse[iPathK];
iPathEndX = iPathStartX;
int iPathEndY = iPathEndX - iPathK;
while (iPathEndX < A.Length && iPathEndY < B.Length && A[iPathEndX + 1] == B[iPathEndY + 1])
{
iPathEndX++;
iPathEndY++;
}
//Length of an SES is 2D.
return(2 * D);
}
}
}
}
//We should never get here if the algorithm is coded correctly.
Debug.Assert(false);
return(-1);
}
