Lennot

from heapq import heappush, heappop
 
class Node:
    def __init__(self):
        self.neighbors = [] # tuple, [noden numero, matkan hinta]
        self.stepNum = 0 # monesko node reitillä
    
    # onko seuraava lento ilmainen
    def nextFree(node):
        return node.stepNum % 2 != 0
 
# etsi pienin hinta        
def dijkstraSearch(nodes, startNode, endNode, infiniteVal, checkCycles, startingDistance, startingStep):
    q = []
    t = [0] * len(nodes)
    e = [infiniteVal] * len(nodes)
    e[startNode] = startingDistance
    cycleNodes = []
    nodes[startNode].stepNum = startingStep
    
    heappush(q, (startingDistance, startNode))
    
    while len(q) != 0:
        current = heappop(q)
        
        x = current[0] # etäisyysarvio
        s = current[1] # noden numero
        # print ('In node {} with distance {}'.format(s + 1, x))
        if t[s] != 0:
            continue
        t[s] = 1
        
        for i in range(0, len(nodes[s].neighbors)):
            u = nodes[s].neighbors[i][0] # tämänhetkisen viereisen noden numero
            # print ('Checking subnode {}'.format(u + 1))
            dist = 0
            if not nodes[s].nextFree():
                dist = nodes[s].neighbors[i][1]
            if x + dist < e[u]:
                e[u] = x + dist
                nodes[u].stepNum = nodes[s].stepNum + 1
                heappush(q, (e[u], u))
                # print ('Set node {} to {}'.format(u + 1, e[u]))
            elif checkCycles and ((nodes[s].stepNum + 1) % 2 != nodes[u].stepNum % 2):
                cycleNodes.append((u, x + dist, nodes[s].stepNum + 1))
                # print ('Forced node {}'.format(u + 1))
                
    distances = []
    distances.append(e[endNode])
    
    if checkCycles:        
        for i in range(0, len(cycleNodes)):
            for j in range(0, len(nodes)):
                nodes[j].stepNum = 0
            distances.append(dijkstraSearch(nodes, cycleNodes[i][0], endNode, infiniteVal, False, cycleNodes[i][1], cycleNodes[i][2]))
            
    return min(distances)
    
 
cityCount, flightCount = [int(x) for x in input().split(" ")]
 
nodes = [Node() for i in range(0, cityCount)] # kaupunki i on node i - 1 ts. kaupunki 1 on nodes[0]
 
for i in range(0, flightCount):
    startCity, endCity, price = [int(x) for x in input().split(" ")]
    nodes[startCity - 1].neighbors.append((endCity - 1, price))
 
infiniteVal = 1000000000 * flightCount + 1
cheapest = dijkstraSearch(nodes, 0, cityCount - 1, infiniteVal, True, 0, 0)
 
print (cheapest)

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: WRONG ANSWER

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: WRONG ANSWER

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 12

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 13

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 14

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 15

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 16

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 17

Group: 3

Verdict: TIME LIMIT EXCEEDED