solution to codility challenge https://codility.com/programmers/challenges/magnesium2014

longest_path.py

def solution(N, A, B, C):
    edges = [(C[i],A[i],B[i]) for i in xrange(len(A))]
    edges.sort(key=lambda e: e[0])
    maxLenAt = [0]*N
    costAt = [0]*N
   
    def updatePath(u,costu,lenu, v,costv, lenv, cost):
        if costu < cost and lenu+1 > lenv:
            maxLenAt[v] = lenu+1 
            costAt[v] = cost
        elif costu == cost and lenv == 0:
            maxLenAt[v] = 1
            costAt[v] = cost
            
    for cost,u,v in edges:
        cost_u,cost_v = costAt[u], costAt[v]
        len_u, len_v = maxLenAt[u], maxLenAt[v]
        updatePath(u,cost_u,len_u, v, cost_v, len_v,cost)
        updatePath(v, cost_v, len_v, u,cost_u,len_u,cost)
    return max(maxLenAt)