Question

How to find an element that appears once in an array of elements that appears three times in C#

Answer 1

using System;
using System.Collections.Generic;

class FindElementThatAppearsOnceInArray_CSharp
{
    public static int FindElementThatAppearsOnceInArray(int[] arr)
    {
        Dictionary<int, int> map = new Dictionary<int, int>();

        foreach (int x in arr) {
            if (map.ContainsKey(x)) {
                map[x]++;
            }
            else {
                map[x] = 1;
            }
        }

        foreach (KeyValuePair<int, int> entry in map) {
            if (entry.Value == 1) {
                return entry.Key;
            }
        }

        return -1;
    }

    public static void Main(string[] args)
    {
        int[] arr = new int[] { 3, 5, 5, 2, 7, 3, 2, 8, 8, 3, 2, 5, 8 };

        Console.WriteLine(FindElementThatAppearsOnceInArray(arr));
    }
}




/*
run:
 
7
 
*/

 

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Answer 2

using System;

class FindElementThatAppearsOnceInArray_Csharp
{
    public static int FindElementThatAppearsOnceInArray(int[] arr) {
        int result = 0;

        for (int i = 0; i < 32; i++) {
            int sum = 0;
            foreach (int num in arr) {
                sum += (num >> i) & 1;
            }
            sum %= 3;
            result |= sum << i;
        }

        return result;
    }

    public static void Main(string[] args)
    {
        int[] arr = new int[] { 3, 5, 5, 2, 7, 3, 2, 8, 8, 3, 2, 5, 8 };

        Console.WriteLine(FindElementThatAppearsOnceInArray(arr));
    }
}





/*
run:
 
7
 
*/

 

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