Most Frequent Integer

Find the most frequent integer(s) in an array.

Example 1: Given the below array, your method should return (7).

int[] arr = {1,2,3,4,5,6,7,7,7,7};

Example 2: Given the below array, your method should return (5) -> (6).

int[] arr = {1,2,2,3,4,5,5,5,6,6,6,7};

Solution

public LinkedList<Integer> findMode(int[] arr) {
    HashMap<Integer,Integer> hmap = new HashMap<Integer,Integer>();

    // Get counts for each int in arr
    for (int i : arr) {
        Integer count = map.get(i);
        hmap.put(i, count != null ? count+1 : 1);   // if int exists in hmap, increment
                                                    // otherwise add int with count of 1
    }

    // Find the mode(s)
    Integer maxCount = 0;
    LinkedList<Integer> maxKeys = new LinkedList<Integer>();
    Set<Integer> keySet = hmap.keySet();

    for (Integer k : keySet) {
        Integer val = hmap.get(k);
        if (val == maxCount)
            maxKeys.add(k);
        else if (val > maxCount) {  //found new max count in hmap
            maxKeys.clear();    //remove ints with old (smaller) maxCount
            maxKeys.add(k);
            maxCount = val;     //update with new max count value
        }
    }

    return maxKeys;
}