How to Sort Two Arrays with Array.Sort in .NET

Tiago Soczek — Sat, 18 Jan 2025 15:39:26 +0000

The method Array.Sort(array, array) has been available since .NET Framework 2.0, but I recently discovered it. It allows sorting a pair of arrays, with the first array used as keys and the second as values:

var keys = ['A','C','B'];
var values = [1,3,2];

Array.Sort(keys, values);

// keys = ['A','B','C']
// values = [1,2,3]

The result is that both arrays are sorted, preserving the relationship between keys and values. Additionally, you can provide a custom Comparer to define your own sorting logic.

While Array.Sort is not commonly seen in "commercial" code nowadays, I found this feature quite interesting and versatile!

Sliding Window Median with .NET 9

Tiago Soczek — Sat, 18 Jan 2025 15:01:43 +0000

.NET 9 introduced support for the Remove method in PriorityQueue:

boolean removed = priorityQueue.Remove(element, out var _, out var _);

This method is particularly useful for solving the Sliding Window Median problem on LeetCode. By leveraging two heaps (a max-heap and a min-heap, implemented with PriorityQueue), it allows for the immediate removal of elements that fall out of the sliding window. However, the time complexity of the Remove operation is linear, $O (n)$ .

public class Solution {
    // For a max-heap with negative values, define a custom comparer instead of using the negative priority trick
    private PriorityQueue<int, int> maxHeap = new(Comparer<int>.Create((a, b) => b.CompareTo(a)));
    private PriorityQueue<int, int> minHeap = new();

    public double[] MedianSlidingWindow(int[] nums, int k) {
        var res = new List<double>();

        for(var i = 0; i < nums.Length; i++) {
            if (i >= k) {
                Remove(nums[i-k]);
            }

            Add(nums[i]);

            if (i >= k - 1) {
                res.Add(GetMedian());
            }
        }

        return res.ToArray();
    }

    private void Add(int n) {
        // Another feature in PriorityQueue: https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.priorityqueue-2.enqueuedequeue?view=net-9.0
        var m = maxHeap.EnqueueDequeue(n, n);
        minHeap.Enqueue(m, m);

        if (minHeap.Count - 1 > maxHeap.Count)
        {
            m = minHeap.Dequeue();
            maxHeap.Enqueue(m, m);
        }
    }

    private void Remove(int n) {
        // Support for the Remove method, introduced in .NET 9
        if (!minHeap.Remove(n, out var _, out var _)) {
            maxHeap.Remove(n, out var _, out var _);
        }
    }

    private double GetMedian() {
        if (minHeap.Count != maxHeap.Count) {
            return minHeap.Peek();
        }

        // Cast to long to prevent overflow when adding values (e.g., int.MaxValue + int.MaxValue)
        return ((long)minHeap.Peek() + maxHeap.Peek()) / 2.0;
    }
}

Learn more about PriorityQueue in .NET:

DEV Community: Tiago Soczek

How to Sort Two Arrays with Array.Sort in .NET

Sliding Window Median with .NET 9