# 99 questions/Solutions/88

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Revision as of 23:30, 5 March 2011 by Jagbolanos (talk | contribs) (Connected components in Haskell)

```
import Data.List
type Node = Int
type Edge = (Node,Node)
type Graph = ([Node],[Edge])
depthfirst :: Graph -> Node -> [Node]
depthfirst (v,e) n
| [x|x<-v,x==n] == [] = []
| otherwise = dfrecursive (v,e) [n]
dfrecursive :: Graph -> [Node] -> [Node]
dfrecursive ([],_) _ = []
dfrecursive (_,_) [] = []
dfrecursive (v,e) (top:stack)
| [x|x<-v,x==top] == [] = dfrecursive (newv, e) stack
| otherwise = top : dfrecursive (newv, e) (adjacent ++ stack)
where
adjacent = [x | (x,y)<-e,y==top] ++ [x | (y,x)<-e,y==top]
newv = [x|x<-v,x/=top]
connectedcomponents :: Graph -> [[Node]]
connectedcomponents ([],_) = []
connectedcomponents (top:v,e)
| remaining == [] = [connected]
| otherwise = connected : connectedcomponents (remaining, e)
where
connected = depthfirst (top:v,e) top
remaining = (top:v) \\ connected
```

You can call it:

```
connectedcomponents ([1,2,3,4,5],[(2,3),(3,4),(1,5)])
```