missing term in Arithmetic Progression

Question

1.50/5 (7 votes)

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Please provide me an algorithm or code to find a missing term in Arithmetic Progression in c#.
Ex:
1. Input: 1,11,31,41,51
Output: 21

2. Input : 1,3,5,7,11
Output :9

Posted 11-Nov-13 2:39am

raneshtiwari

Updated 28-Aug-14 6:03am

Nelek

v2

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Comments

Zoltán Zörgő 11-Nov-13 8:57am

Homework :(

ZurdoDev 28-Aug-14 13:45pm

Where are you stuck?

2 solutions

Solution 4

This probably should cover all kinds of test cases.

C#

public class Program
    {
        public static void Main(string[] args)
        {
            //your input
            int[] inputArray = new int[] { 1, 11, 31, 41, 61 };
            int difference = 0;
            for (int i = 0; i < (inputArray.Length - 1); i++)
            {
                int first = inputArray[i];
                int second = inputArray[i + 1];
                //find minimum difference of all terms
                if (difference == 0)
                {
                    difference = second - first;
                }
                else
                {
                    difference = Math.Min(difference, (second - first));
                }
            }
            WriteMissingElement(difference, inputArray);
            Console.ReadKey();
        }

        private static void WriteMissingElement(int reqdDifference, int[] input)
        {
            int last = input.Last();
            int nextNumber = input.First() + reqdDifference;

            while (nextNumber != last)
            {
                if (!input.Contains(nextNumber))
                {
                    Console.WriteLine(nextNumber);
                }
                nextNumber = nextNumber + reqdDifference;
            }
        }
    }

Posted 26-Aug-14 2:02am

touchofevil

Updated 26-Aug-14 17:32pm

v3

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Member 9866853 · Accepted Answer · 2015-06-03T18:14:00

C#

public static int GetArithmaticProgression(int[] nums)
{
    // Arithmatic Progression (AP)-
    // Example 1: 5 13 17 21 25; Missing AP is 9 between 5 and 13 with common difference 4
    // Example 2: 9 14 24 29 34; Missing AP is 19 between 14 and 24 with common difference 5
    // Example 3: 25 28 31 37 40 43: Missing AP is 34 between 31 and 37 with common difference 3
    // Namira
    int[] iDiff = new int[nums.Length - 1];

    for (int k = 0; k < nums.Length; k++)
    {
        // Which 2 numbers have the largest differnce?
        if (k > 0)
            iDiff[k - 1] = nums[k] - nums[k - 1]; // 13 - 5 (8) 17 - 13 (4)
    }

    int min = iDiff.Min(); // This is the common differnce
    int max = iDiff.Max(); // This is the largest difference between numbers.

    // Get the index of 1st number with the missing AP
    var indexAtMax = iDiff.ToList().IndexOf(max);

    // Missing number is:
    return nums[indexAtMax] + min;
}