Reconstruct Itinerary

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c++

class Solution {public:    vector<string> findItinerary(vector<pair<string, string>> tickets) {        if (tickets.empty()) return vector<string>();        unordered_map<string, multiset<string>> graph;        for (auto &v : tickets) {            graph[v.first].insert(v.second);        }        stack<string> dfs;        dfs.push("JFK");        vector<string> res;        while (!dfs.empty()){            string cur_node = dfs.top();            if (graph[cur_node].empty()) {                res.push_back(cur_node);                dfs.pop();            }            else {                dfs.push(*graph[cur_node].begin());                graph[cur_node].erase(graph[cur_node].begin());            }        }        reverse(res.begin(), res.end());        return res;    }};

python

class Solution(object):    def findItinerary(self, tickets):        """        :type tickets: List[List[str]]        :rtype: List[str]        """        if not tickets: return []        graph = collections.defaultdict(list)        for a, b in sorted(tickets)[::-1]:            graph[a].append(b)        dfs = ['JFK']        res = []        while dfs:            cur_node = dfs[-1]            if not graph[cur_node]:                res.append(dfs.pop())            else:                dfs.append(graph[cur_node].pop())        return res[::-1]

reference:
1\ https://leetcode.com/discuss/85439/short-iterative-solution-explanation-recursive-backtracking
2\ Introduction to Algorithms, Chapter 22: Graph Algorithms

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