CODEWITHSUNDEEP
javaarraylist
lord_sneed
lord_sneed

Reputation: 824

Find Max Number(s) in an ArrayList (Possibility of More Than One Max Value)

I would like to find the index/indices that hold the maximum value in an ArrayList. I want to preserve the order that the numbers are in (in other words no sorting) because I want to keep track of what index had what value. The values are from a random number generator and there is the possibility of having two (or more) indices sharing the same maximum value.

An example ArrayList:

12, 78, 45, 78

0,1,2,3 <- indices

(So indices, 1 and 3 contain the values that have the max values. I want to maintain the fact that indices 1 and 3 have the value 78. I do not want to just create a new ArrayList and have indices 0 and 1 of the new ArrayList have the values 78)

Therefore, I want to find all of the indices that have the maximum values because I will be doing something with them to "break" the tie if there is more than one index. So how can I find the indices that contain the maximum value and maintain the index-to-value relationship?

I have written the following methods:

public static ArrayList<Integer> maxIndices(ArrayList<Integer> numArrayList) {
// ???  
    return numArrayList;
}

public static void removeElement(ArrayList<Integer> numArrayList, int index) {
    numArrayList.remove(index);
}

public static int getMaxValue(ArrayList<Integer> numArrayList) {
    int maxValue = Collections.max(numArrayList);
    return maxValue;
}

public static int getIndexOfMaxValue(ArrayList<Integer> numArrayList, int maxVal) {
    int index = numArrayList.indexOf(maxVal);
    return index;
}

Upvotes: 2

Views: 6845

Answers (2)

卢声远 Shengyuan Lu
卢声远 Shengyuan Lu

Reputation: 32004

O(n) solution:

   public static List<Integer> maxIndices(List<Integer> l) {
        List<Integer> result = new ArrayList<Integer>();
        Integer candidate = l.get(0);
        result.add(0);

        for (int i = 1; i < l.size(); i++) {
            if (l.get(i).compareTo(candidate) > 0) {
                candidate = l.get(i);
                result.clear();
                result.add(i);
            } else if (l.get(i).compareTo(candidate) == 0) {
                result.add(i);
            }
        }
        return result;
    }

Upvotes: 1

Jiyda Moussa
Jiyda Moussa

Reputation: 925

public static ArrayList<Integer> maxIndices(ArrayList<Integer> list) {
    List<Integer> indices = new ArrayList<Integer>();
    int max =  getMaxValue(list);
    for (int i = 0; i < list.size(); i++) {
       if(list.get(i) == max) {
           indices.add(list.get(i));
        }
     }

     return indices;
}

Upvotes: 3

Related Questions