# 99 questions/Solutions/89

### From HaskellWiki

import Data.List type Node = Int type Edge = (Node,Node) type Graph = ([Node],[Edge]) dfsbipartite :: Graph -> [(Node, Int)] -> [Node] -> [Node] -> Bool dfsbipartite ([],_) _ _ _ = True dfsbipartite (_,_) [] _ _ = True dfsbipartite (v,e) ((nv, 0):stack) odd even | [x|x<-v,x==nv] == [] = dfsbipartite (v, e) stack odd even | [] == intersect adjacent even = dfsbipartite (newv, e) ([(x,1)|x<-adjacent] ++ stack) odd (nv : even) | otherwise = False where adjacent = [x | (x,y)<-e,y==nv] ++ [x | (y,x)<-e,y==nv] newv = [x|x<-v,x/=nv] dfsbipartite (v,e) ((nv, 1):stack) odd even | [x|x<-v,x==nv] == [] = dfsbipartite (v, e) stack odd even | [] == intersect adjacent odd = dfsbipartite (newv, e) ([(x,0)|x<-adjacent] ++ stack) (nv : odd) even | otherwise = False where adjacent = [x | (x,y)<-e,y==nv] ++ [x | (y,x)<-e,y==nv] newv = [x|x<-v,x/=nv] bipartite :: Graph -> Bool bipartite ([],_) = True bipartite (top:v,e) = dfsbipartite (top:v, e) [(top,0)] [] []

You can call it:

bipartite ([1,2,3,4,5],[(1,2),(2,3),(1,4),(3,4),(5,2),(5,4)])