Reduce Array Size to The Half

Array, Hash Table

You are given an integer array arr. You can choose a set of integers and remove all the occurrences of these integers in the array. Return the minimum size of the set so that at least half of the integers of the array are removed.

Solutions

Easy solution, count each number occurrence.

Approach – Using Hash Table

Run loop and add element occurrence count into hash table.

Steps

1. Run a loop up to length of array element.

2. Add increment element occurrence count.

3. Take sum and count variables.

4. Run loop over hash table descending by value.

5. Check if sum of element value is greater than half of array length and return count, else increment count value.

public class Solution
{
   public int MinSetSize(int[] arr)
    {

        int mid = arr.Length / 2;
        Dictionary<int, int> map = new Dictionary<int, int>();
        for (int i = 0; i < arr.Length; i++)
        {
            var key = arr[i];
            if (map.ContainsKey(key))
            {
                map[key]++;
            }
            else
            {
                map[key] = 1;
            }
        }
        int count = 0;
        int sum = 0;

        foreach (var item in map.OrderByDescending(x=>x.Value))
        {
            sum += item.Value;
            count++;
            if (sum >= mid) return count;

        }
        return 0;
    }
}

Complexity

• Time complexity: O(N log N)

• Space complexity: O(1)