Python/graphs/kahns_algorithm_long.py

# Finding longest distance in Directed Acyclic Graph using KahnsAlgorithm
def longestDistance(l):
    indegree = [0] * len(l)
    queue = []
    longDist = [1] * len(l)

    for key, values in l.items():
        for i in values:
            indegree[i] += 1

    for i in range(len(indegree)):
        if indegree[i] == 0:
            queue.append(i)

    while(queue):
        vertex = queue.pop(0)
        for x in l[vertex]:
            indegree[x] -= 1

            if longDist[vertex] + 1 > longDist[x]:
                longDist[x] =  longDist[vertex] + 1

            if indegree[x] == 0:
                queue.append(x)

    print(max(longDist))

# Adjacency list of Graph
l = {0:[2,3,4], 1:[2,7], 2:[5], 3:[5,7], 4:[7], 5:[6], 6:[7], 7:[]}
longestDistance(l)