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### leetcode Reconstruct Itinerary

Given a list of airline tickets represented by pairs of departure and arrival airports [from, to], reconstruct the itinerary in order. All of the tickets belong to a man who departs from JFK. Thus, the itinerary must begin with JFK.

Note:

1. If there are multiple valid itineraries, you should return the itinerary that has the smallest lexical order when read as a single string. For example, the itinerary ["JFK", "LGA"] has a smaller lexical order than ["JFK", "LGB"].
2. All airports are represented by three capital letters (IATA code).
3. You may assume all tickets may form at least one valid itinerary.

Example 1: tickets = [["MUC", "LHR"], ["JFK", "MUC"], ["SFO", "SJC"], ["LHR", "SFO"]] Return ["JFK", "MUC", "LHR", "SFO", "SJC"].

Example 2: tickets = [["JFK","SFO"],["JFK","ATL"],["SFO","ATL"],["ATL","JFK"],["ATL","SFO"]] Return ["JFK","ATL","JFK","SFO","ATL","SFO"]. Another possible reconstruction is ["JFK","SFO","ATL","JFK","ATL","SFO"]. But it is larger in lexical order.

• 从JFK出发。
• 如果有多个解，输出字典序最小的。

• 返回的答案必为n+1，n为tickets的个数

• 一张飞机票只能用一次，所以要计数。（可能重复）

• 字典序最小只需要保证我们遍历的时候从小到大遍历即可。so，建图的时候邻接表边从小到大。

• 所以C++用map, Python 排序后OrderedDict.

C++

Python