leetcode-332-Reconstruct Itinerary

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这道题考的是DFS、有向图、欧拉路径（一笔画问题）、Hierholzer’s 算法。

思路：把问题抽象成一个图，求一笔画路径，还要保持最小序输出，所以应该用multiset存储一个起点的目的地。想到map

class Solution {public:    void dfs(string airport) {        while (map1[airport].size()) {            string temp = *map1[airport].begin();            map1[airport].erase(map1[airport].begin());            dfs(temp);        }        ret.push_back(airport);    }    map<string, multiset<string>> map1;    vector<string> ret;    vector<string> findItinerary(vector<pair<string, string>> tickets) {        for (auto i : tickets) {            map1[i.first].insert(i.second);        }        dfs("JFK");        return vector<string>(ret.rbegin(), ret.rend());    }};

另外，priority_queue也是可以的：
C++代码：

class Solution {public:    void dfs(string airport) {        while (map1[airport].size()) {            string temp = (map1[airport]).top();            map1[airport].pop();            dfs(temp);        }        ret.push_back(airport);    }    map<string, priority_queue<string,vector<string>,greater<string>>> map1;    vector<string> ret;    vector<string> findItinerary(vector<pair<string, string>> tickets) {        for (auto i : tickets) {            map1[i.first].push(i.second);        }        dfs("JFK");        return vector<string>(ret.rbegin(), ret.rend());    }};

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