Problem of the Day
A new programming or logic puzzle every Mon-Fri

You are given an array of unsorted integers. The numbers of this integer contain an odd number of occurrences of all the numbers except for one. One number occurs an even number of times. Can you figure out which number occurs an even number of times?

For bonus solve it without sorting the array.

[7,4,2,6,8,9,2,4,4,5,2,7]

Answer: 7

Comments:

• Ben - 11 years, 1 month ago

  C#

  using System;
  using System.Linq;
  
  namespace EvenOccurances
  {
      class Program
      {
          static void Main(string[] args)
          {
              int[] arr = new int[] { 7, 4, 2, 6, 8, 9, 2, 4, 4, 5, 2, 7 };
              var evens = arr.Distinct().Where(x => arr.Where(y => y == x).Count() % 2 == 0);
              Console.WriteLine(string.Join(",", evens.Select(x => x.ToString())));
              Console.Read();
          }
      }
  }
  

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• John - 11 years, 1 month ago

  function listOfEvenOccurances(arr) {
    return arr.reduce(function(p,c) {
        p[c]=p[c]?p[c]+1:1; return p;
      },[]).reduce(function(p,c,i) {
        if(c%2==0)
          p.push(i);
        return p;
      },[]);
  }
  

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• Vinicius Pires - 11 years, 1 month ago

  a = [7,4,2,6,8,9,2,4,4,5,2,7];
  map = {};
  
  for (var i=0;i<a.length;i++) {
    var cur = a[i];
    if ( ! map[cur] ) {
      map[cur] = 0;
    }
    map[cur]++;
  }
  
  var answer;
  for(var j in map){
    if (map[j] % 2 == 0) {
      answer = parseInt( j );
      break;
    }
  }
  

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• PyBanana - 11 years, 1 month ago

  def getEvenOccurances(integers):
      return set([i for i in integers if integers.count(i) % 2 == 0])
  

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