public static Coordinate FindElement2(int[][] matrix, Coordinate origin, Coordinate dest, int x)
{
if (!origin.Inbounds(matrix) || !dest.Inbounds(matrix))
{
return null;
}
if (matrix[origin.row][origin.column] == x)
{
return origin;
}
else if (!origin.IsBefore(dest))
{
return null;
}
/* Set start to start of diagonal and end to the end of the diagonal. Since
* the grid may not be square, the end of the diagonal may not equal dest.
*/
Coordinate start = (Coordinate)origin.Clone();
int diagDist = Math.Min(dest.row - origin.row, dest.column - origin.column);
Coordinate end = new Coordinate(start.row + diagDist, start.column + diagDist);
Coordinate p = new Coordinate(0, 0);
/* Do binary search on the diagonal, looking for the first element greater than x */
while (start.IsBefore(end))
{
p.SetToAverage(start, end);
if (x > matrix[p.row][p.column])
{
start.row = p.row + 1;
start.column = p.column + 1;
}
else {
end.row = p.row - 1;
end.column = p.column - 1;
}
}
/* Split the grid into quadrants. Search the bottom left and the top right. */
return PartitionAndSearch(matrix, origin, dest, start, x);
}