> For the complete documentation index, see [llms.txt](https://docs-57.gitbook.io/data-structure-and-algorithms/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs-57.gitbook.io/data-structure-and-algorithms/problems/array/reduce-array-size-to-the-half.md).

# Reduce Array Size to The Half

{% hint style="info" %}
Array, Hash Table
{% endhint %}

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.

```csharp
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)`


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs-57.gitbook.io/data-structure-and-algorithms/problems/array/reduce-array-size-to-the-half.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.