Traverse transitive keys in Map

Question

I have Map<String, String> which contains elements like: {“a”=”b”, “b”=”c”, “c”=”d”, “z”=”y”, …}.

I need a method:

List<String> getTransitiveKeys(String startKey);// assuming the map is visible somehow as `map`

When getTransitiveKeys(“a”) is called, it will return [“a”, “b”, “c”]. When getTransitiveKeys (“z”) is called, it will return [“z”].

Recursion needed in the method?

Thanks!

Just looks like a homework. I just abstract the problem and want a neat way to implement the function. — 卢声远 Shengyuan Lu, Jan 17 '11 at 08:18

lweller · Accepted Answer · 2011-01-17T07:45:20.913

4

List<String> getTransitiveKey(String key) {
   List<String> result = new LinkedList<String>();
   while(map.containsKey(key)) {
    // avoid endless loops
    if(result.contains(key)) {
      break;
    }

    result.add(key);  
    key = map.get(key)
  }
  return result;
}

edited Jan 17 '11 at 07:45

answered Jan 17 '11 at 07:37

lweller

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score 0 · Answer 2 · answered Jan 17 '11 at 07:42

0

why recursion ? just a single loop

while(map.get(startKey) != null) {
    startKey =  map.get(startKey);
}

answered Jan 17 '11 at 07:42

Traverse transitive keys in Map

2 Answers2