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February 11, 2016 12:16
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Codingame : Skynet The Virus Python
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import sys, math | |
class Node(object): | |
'''Class representing a node of the network, each node as : | |
a unique id, constant | |
a list of neighbour nodes''' | |
def __init__(self, n =0): | |
self.n = n | |
self.neighb = [] | |
def addNeighb(self, m): | |
self.neighb.append(m) | |
def removeNeighb(self, m): | |
self.neighb.remove(m) | |
class Path(object): | |
'''class representing a path in the network, by a list of node''' | |
def __init__(self, begin, end, nodes): | |
'''This constructor builds a shortest path in the network described by | |
nodes, between begin and end''' | |
self.p = [] | |
N = len(nodes) | |
# explored[i] is True <=> node i has been visited | |
# prec[i] = j <=> node i has been visited coming from node j | |
explored, prec = [], [] | |
for i in range(N): | |
explored.append(False) | |
prec.append(-1) | |
explored[begin.n] = True | |
# A BFS is performed starting from node begin, until finding node end | |
q, n = [], None | |
q.append(begin) | |
while len(q) != 0: | |
n = q.pop() | |
if n == end: | |
break | |
else: | |
for m in n.neighb: | |
if not explored[m.n]: | |
explored[m.n] = True | |
prec[m.n] = n | |
q[0:0] = [m] | |
# if the queue is empty before finding end, there is no path | |
# else a shortest path is identified by backtracking | |
if n == end: | |
while n != begin: | |
self.p[0:0] = [n] | |
n = prec[n.n] | |
self.p[0:0] = [n] | |
def length(self): | |
return len(self.p) | |
def addFirst(self, n): | |
self.p[0:0] = [n] | |
def getNode(self, i): | |
return self.p[i] | |
def cut(n1, n2): | |
'''removes the edge between node n1 and n2''' | |
n1.removeNeighb(n2) | |
n2.removeNeighb(n1) | |
print("{} {}".format(n1.n, n2.n)) | |
# number of nodes, links and exits | |
N, L, E = [int(i) for i in input().split()] | |
# initializing the array of nodes and linking them | |
nodes = [] | |
for i in range(N): | |
nodes.append(Node(i)) | |
for i in range(L): | |
N1, N2 = [int(j) for j in input().split()] | |
nodes[N1].addNeighb(nodes[N2]) | |
nodes[N2].addNeighb(nodes[N1]) | |
# initializing the array of exits | |
exits = [] | |
for i in range(E): | |
exits.append(nodes[int(input())]) | |
while 1: | |
# each turn, identifies one of the shortest paths from Skynet Agent | |
# to each exit node (by a Breadth First Search), then cuts the shortest | |
SI = int(input()) | |
shortestPaths = [] | |
minLength = 9999999 | |
pathToCut = None | |
for i in range(E): | |
shortestPaths.append(Path(nodes[SI], exits[i], nodes)) | |
length = shortestPaths[i].length() | |
if (length != 0) and (length < minLength): | |
minLength = length | |
pathToCut = shortestPaths[i] | |
cut(pathToCut.getNode(0), pathToCut.getNode(1)) |
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