what might be the mistake?

i checked- a) whether skyscraper lies in between line and s
                   b) whether s,a and b really makes a plane
                   c) my algo is like that

- for each skyscraper
        - for each side
               calculate interval if any
           then total interval for that sky scrapper if any
union all such intervals from each sky scrapper.
find the first point which is on the right border of some sky scrapper but not through any.

      is this test precision error or did i forget to check something?

      please help me.

              -thanks in advance

please, guys let me have some useful test cases.
it would be really appreciated.