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ListDifference.java
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ListDifference.java
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/*
Given two lists, return a lists of lists containing the difference between the lists.
Example: a[1, 1, 2, 3, 4], b[1, 3, 5, 6] => [1, 2, 4], [5, 6]
Storage: O(a + b)
Runtime: O(a + b)
*/
public List<List<T>> diff(List<T> a, List<T> b)
{
if (a == null || b == null)
{
throw new IllegalArgumentException();
}
HashMap<T, Integer> aMap = createMap(a);
HashMap<T, Integer> bMap = createMap(b);
List<List<T>> tgt = new ArrayList<ArrayList<T>>();
ArrayList<T> aNotB = diffBetweenLists(aMap, bMap);
ArrayList<T> bNotA = diffBetweenLists(bMap, aMap);
tgt.add(aNotB);
tgt.add(bNotA);
return tgt;
}
public HashMap<T, Integer> createMap(List<T> a)
{
// O(a)
HashMap<T, Integer> tgt = new HashMap<>();
for (T i : a)
{
if (tgt.contains(i))
{
tgt.put(i, tgt.get(i) + 1);
}
else
{
tgt.put(i, 1);
}
}
return tgt;
}
public ArrayList<T> diffBetweenLists(HashMap<T, Integer> aMap, HashMap<T, Integer> bMap)
{
ArrayList<T> aNotB = new ArrayList<T>;
// O(b)
for (Map.Entry<T, Integer> entry : aMap.entrySet())
{
int freqA = entry.getValue();
int valueA = entry.getKey();
int freqB = 0;
if (bMap.contains(valueA))
{
freqB = bMap.get(valueA);
}
for (int i = 1; i <= freqA - freqB; i++)
{
aNotB.add(valueA);
}
}
return aNotB;
}