Java tricky 4 lines using one set
[\n["London","New York"]\n["New York","Lima"]\n["Lima","Sao Paulo"]\n]\n\nObeservation : destination city will always be the right one\n\nwe traverse the input 
[\n["London","New York"]\n["New York","Lima"]\n["Lima","Sao Paulo"]\n]\n\n**Obeservation :** destination city will always be the right one\n\nwe traverse the input for two times\nfirst time, we add all the cities on the right side to a set\nsecond time, we check if the city occurs on the left side, if so, remove it from the set\nresult will be the city left in the set\n\n```\nclass Solution {\n    public String destCity(List<List<String>> paths) {\n        Set<String> set= new HashSet<>();\n        for (List<String> l: paths) set.add(l.get(1));\n        for (List<String> l: paths) set.remove(l.get(0));\n        return set.iterator().next();\n    }\n}\n```
[]