332. Reconstruct Itinerary

"""
        key is to store tickets information in default dictionary in lexical order.
        and what to do when ran into destination before going through all tickets. 
        if encounter destination, add to result list first. 
        then reverse the result in the end. 
        """
iterative solution 

class Solution(object):
    def findItinerary(self, tickets):
        """
        :type tickets: List[List[str]]
        :rtype: List[str]
        """
        targets=collections.defaultdict(list)
        for a , b in sorted(tickets)[::-1]:
            targets[a]+=[b]
        #print targets
        route =[]
        stack=['JFK']
        while stack:
            while targets[stack[-1]]:
                stack.append(targets[stack[-1]].pop())
            route.append(stack.pop())
        return route[::-1]


recursive solution 
class Solution(object):
    def findItinerary(self, tickets):
        """
        :type tickets: List[List[str]]
        :rtype: List[str]
        """
        targets=collections.defaultdict(list)
        for a , b in sorted(tickets)[::-1]:
            targets[a]+=[b]
        #print targets
        route =[]
        def visit(airport):
            
            while targets[airport]:
                visit(targets[airport].pop())
            route.append(airport)
        visit('JFK')
        return route[::-1]