题目：

题解：

func findItinerary(tickets [][]string) []string {
    var (
        m  = map[string][]string{}
        res []string
    )
    
    for _, ticket := range tickets {
        src, dst := ticket[0], ticket[1]
        m[src] = append(m[src], dst)
    }
    for key := range m {
        sort.Strings(m[key])
    }

    var dfs func(curr string)
    dfs = func(curr string) {
        for {
            if v, ok := m[curr]; !ok || len(v) == 0 {
                break
            }
            tmp := m[curr][0]
            m[curr] = m[curr][1:]
            dfs(tmp)
        }
        res = append(res, curr)
    }

    dfs("JFK")
    for i := 0; i < len(res)/2; i++ {
        res[i], res[len(res) - 1 - i] = res[len(res) - 1 - i], res[i]
    }
    return res
}