Terminated due to timeout for my hacker rank solution

rahul uday :

Hello all please check the problemHackerRank Problem Statement

This is my solution for the above problem(link)

static int migratoryBirds(List<Integer> arr) {
    int ar[]=new int[arr.size()];
    for(int i=0;i<arr.size();i++){
        ar[i] = Collections.frequency(arr,arr.get(i));
        // ar[i] = obj.occuranceOfElement(arr,arr.get(i));
    }
    int maxAt = 0;
    for (int i = 0; i < ar.length; i++) {
        maxAt = ar[i] > ar[maxAt] ? i : maxAt;
    }
    return arr.get(maxAt);
}

my code is unable to handle when the array size is bigger,example 17623 elements in array.

Terminated due to timeout

The problem is in the second for loop which iterates over the array and gives me the index of the largest number in the array.Is there any other way that I could increase the performance.

oleg.cherednik :

Your problem is in this part:

for(int i = 0; i < arr.size(); i++)
    ar[i] = Collections.frequency(arr, arr.get(i));

This is O(N²): Collections.frequency() iterates over whole list to calculate frequency for only one element. Manually, you can iterate over the list to calculate frequencey for all elements.

Moreover, ther're only 5 birds, so you need only 5 length array.

static int migratoryBirds(int[] arr) {
    int max = 1;
    int[] freq = new int[6];

    for (int val : arr)
        freq[val]++;

    for (int i = 2; i < freq.length; i++)
        max = freq[i] > freq[max] ? i : max;

    return max;
}