quicksort.cs

using System;
public static class Sort {
    public static void quicksort(Span<int> arr){
        void swap(Span<int> s, int i, int j){
            var tmp = s[i];
            s[i] = s[j];
            s[j] = tmp;
        }

        int partition(Span<int> s) {
            var i=0;
            var pivot = s[0];
            for(int j = 1; j < s.Length; j++){
                if(pivot > s[j]) {
                    swap(s, i, j);
                    i++;
                }
            }
            if(pivot > s[s.Length - 1]) {
                swap(s, 0, s.Length - 1);
            }
            return i;
        }

        if (arr.Length <= 1) return;
        var p = partition(arr);
        if(p-1>0) quicksort(arr.Slice(0, p - 1));
        if(p+1<arr.Length) quicksort(arr.Slice(p + 1));
    }
}