K-th Element of Two Sorted Arrays

k-th-element-two-sorted-arrays.cs

using System;
using System.Collections.Generic;

namespace prob
{
    class Program
    {
        static void Main(string[] args)
        {
          //Test input
            var x = Find(
                new int[] { 1, 2, 10, 24, 36, 46, 47, 48, 49, 50 },
                0,
                9,
                new int[] { 2, 2, 2, 3, 4, 6, 10, 20 },
                0,
                7,
                7);
                
            Console.WriteLine(x);
        }

        static int up(int s, int e, int len)
        {
            return (s + Math.Abs(e-s) / 2)%len;
        }

        static int Find(int[] a, int s1, int e1, int[] b, int s2, int e2, int k)
        {
            var m = up(s1, e1, a.Length);
            var n = up(s2, e2, b.Length);

            if(s1 == e1)
                return b[n];
            if(s2==e2)
                return a[m];

            var t = m+n+2; //as the index starts from 0

            if (t > k)
            {
                if (a[m] > b[n])
                {
                    return Find(a, s1, m, b, s2, e2, k);
                }
                else
                {
                    return Find(a, s1, e1, b, s2, n, k);
                }
            }
            else
            {
                if (a[m] < b[n])
                {
                    return Find(a, m + 1, e1, b, s2, e2, k);
                }
                else
                {
                    return Find(a, s1, e1, b, n+1, e2, k);
                }
            }
        }
    }
}