Question

How to find the minimum distance between two numbers in an array with C#

Answer 1

using System;

public static class ArrayDistance
{
    /// <summary>
    /// Finds the minimum distance between two target values in an array.
    /// </summary>
    /// <param name="numbers">Input array.</param>
    /// <param name="target1">First target value.</param>
    /// <param name="target2">Second target value.</param>
    /// <returns>
    /// The minimum distance between the target values,
    /// or -1 if no valid pair exists.
    /// </returns>
    /// <exception cref="ArgumentNullException">
    /// Thrown when numbers is null.
    /// </exception>
    public static int FindMinimumDistance(int[] numbers, int target1, int target2)
    {
        if (numbers == null) {
            throw new ArgumentNullException("numbers");
        }

        // Special case:
        // Find the minimum distance between consecutive
        // occurrences of the same value.
        if (target1 == target2) {
            return FindMinimumDistanceForSameValue(numbers, target1);
        }

        int lastSeenIndex = -1;
        int minimumDistance = int.MaxValue;

        for (int i = 0; i < numbers.Length; i++)
        {
            int currentValue = numbers[i];

            // Skip irrelevant values.
            if (currentValue != target1 && currentValue != target2) {
                continue;
            }

            /*
             * If we previously encountered one of the target
             * values and the current value is the other target,
             * update the minimum distance.
             */
            if (lastSeenIndex >= 0 && currentValue != numbers[lastSeenIndex])
            {
                int distance = i - lastSeenIndex;

                if (distance < minimumDistance) {
                    minimumDistance = distance;
                }
            }

            // Remember the most recent occurrence.
            lastSeenIndex = i;
        }

        return minimumDistance == int.MaxValue
            ? -1
            : minimumDistance;
    }

    /// <summary>
    /// Finds the minimum distance between consecutive
    /// occurrences of the same value.
    /// </summary>
    private static int FindMinimumDistanceForSameValue(int[] numbers, int target)
    {
        int previousIndex = -1;
        int minimumDistance = int.MaxValue;

        for (int i = 0; i < numbers.Length; i++)
        {
            if (numbers[i] != target) {
                continue;
            }

            if (previousIndex >= 0) {
                int distance = i - previousIndex;

                if (distance < minimumDistance) {
                    minimumDistance = distance;
                }
            }

            previousIndex = i;
        }

        return minimumDistance == int.MaxValue
            ? -1
            : minimumDistance;
    }
}

public class Program
{
    public static void Main()
    {
        int[] numbers = {2, 3, 7, 3, 3, 4, 8, 8, 8, 11, 9, 1, 3};

        int result =
            ArrayDistance.FindMinimumDistance(
                numbers,
                3,
                8);

        if (result >= 0) {
            Console.WriteLine(
                "Minimum distance between 3 and 8: {0}",
                result);
        }
        else {
            Console.WriteLine("No valid pair found.");
        }
    }
}


/*
run:

Minimum distance between 3 and 8: 2

*/

 

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