function to returns the nearest element of array to an integer

Question

I want to make a function that gives an array returns the nearest element to a number.

here is some examples:

int[] arr = new int[] {12, 48, 50, 100};
my_function(1, arr); // returns 12.
my_function(40, arr); // returns 48.
my_function(49, arr); // returns 50; in two element with equal distance, returns greater number
my_function(70, arr); // returns 50.
my_function(10005, arr); // returns 100.

Sorry, I have no idea about how to write this function.

Answer 1

private int GetNearest(int[] array,int number)
{
    return array.OrderBy(x => Math.Abs((long)x - number)).FirstOrDefault();
}

If you want to be sure that the larger number is before smaller number when the absolute difference is the same, add .ThenByDescending(a => a) after OrderBy(x => Math.Abs((long)x - number))

private int GetNearest(int[] array,int number)
{
    return array.OrderBy(x => Math.Abs((long)x - number)).ThenByDescending(a => a).FirstOrDefault();
}

Answer 2

This is a solution without using System.Linq and with O(n) complexity. You just go through array in loop and find a number with minimal difference, abs <= diff condition allows you to return the latest number (50 for 49 instead of 48) in sorted array. If difference equals 0, it means that you find the exact number

var arr = new[] { 12, 48, 50, 100 };

int nearest = GetNearest(1, arr);
nearest = GetNearest(40, arr);
nearest = GetNearest(49, arr);
nearest = GetNearest(70, arr);
nearest = GetNearest(1005, arr);

int GetNearest(int number, int[] array)
{
    int diff = int.MaxValue;
    int result = 0;
    foreach (var item in array)
    {
        var abs = Math.Abs(item - number);
        if (abs == 0)
        {
            result = item;
            break;
        }

        if (abs <= diff)
        {
            diff = abs;
            result = item;
        }
    }

    return result;
}