graph interview

A B  = 5
B D = 6
C D = 3
E F
F G

|


? D

A B

         
   a - c - b - d
 
a -> c
a/b = a/c / b/c
a/d = a/b / b/d
  

a a = 1
a b = ?
a c => a/b b/c
a d => a/b b/d


a is the center point

c - a
b - a
d - a

? a
b c

steps:
(1) build graph  (n)
(2) find connected components (n)
(3) for every component:  (n)
        find a center point x
        convert their relationships to ? - x


(4) query: x, y   (1)
    x and y are not in the same com: return -1
    else:
        x or y is the center point, return v, 1/v
        x/c, y/c -> x/y

  A-B-D-C -> 
  
  E-F-G
  
  
  O(3*N) + O(M)