javascript - Find head of link chain -

using lodash, have created array of pairs, each representing source , destination of link. given path of links, have:

[ [a, b], [a, c], [d, c] ] 

it given first element first link in chain. wanted map pairs key/value map object , go through keys and/or values find head.

simplified algorithm:

keys.contains(a) || values.contains(a) 

if either returns true (excluding pair itself, naturally), not head. so, starting first pair, keys.contains(a) || values.contains(a) returns true not head, , keys.contains(b) || values.contains(b) returns false - must head.

the problem: can't map pairs object, since there might key/value duplicates override each other.

i.e., examples above, resulting object be:

{    a: c,    d: c } 

i know can loop through them, reluctant many loops unless have to...

any ideas of more efficient solution?

i assume source key , destination value. roots of directed graph keys not occur value. (the leafs: vice versa).

a root, d. b , c not. condition should keys.contains(a) && !values.contains(a).

you might not have root @ though if objects point each other ([ [a, b], [b, a] ]) or if points ([ [a, a] ]).

now if eliminate self references, can collect keys , values. roots iterate on keys , test if aren't value. leafs, iterate on values , test if aren't key.

hth, i'm not sure understood question correctly.