Test if the lines can make a closed curve

Hi,

I'm new to VB in GH. 

I got lots of perpendicular lines, some of them can be connected to closed polygons. I want to retrieve those lines and get the polygons.

What i've already done is sorting the lines into x-vector and y-vector, and testing the relations between each 2 lines, and i've taken the index Ix-Iy (2 lists of index)of those who can make a corner. I'm thinking about starting with one of the lines, using the index-x to find another possible index-y, then index-x, then index-y,...until(after at least 4 index) a index-x equals to the first one. But i don't know how should i write the loop, seems to me every time you need to find the next match and it can be endless.

I don't know if i've made myself clear...