Question

How to implement ternary search to find a value in a sorted array with C#

Answer 1

using System;

class TernarySearchDemo
{
    public static int TernarySearch(int l, int r, int key, int[] arr) {
        while (l <= r) {
            int mid1 = l + (r - l) / 3;
            int mid2 = r - (r - l) / 3;

            if (arr[mid1] == key) return mid1;
            if (arr[mid2] == key) return mid2;

            if (key < arr[mid1]) {
                r = mid1 - 1;
            }
            else if (key > arr[mid2]) {
                l = mid2 + 1;
            }
            else {
                l = mid1 + 1;
                r = mid2 - 1;
            }
        }

        return -1; // not found
    }

    static void Main()
    {
        int[] arr = { 1, 2, 8, 14, 15, 64, 78, 89, 99, 100, 110, 123 };

        int toSearch = 89;

        int index = TernarySearch(0, arr.Length - 1, toSearch, arr);

        if (index != -1)
            Console.WriteLine("Element found at index: " + index);
        else
            Console.WriteLine("Element not found.");
    }
}


/*
run:

Element found at index: 7

*/

 

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