Find value that occurs in odd number of elements.

codility-array-pair.js

// codility test prep questions
// For example, in array A such that:
// A[0] = 9 A[1] = 3 A[2] = 9 A[3] = 3 A[4] = 9 A[5] = 7 A[6] = 9
// the elements at indexes 0, 2 and 4 have value 9,
// the elements at indexes 1 and 3 have value 3,
// the element at index 5 has value 7 and is unpaired.

function findPairs(arr){
  var hash = {}
  arr.map((num)=>{
      if(!hash[num]){
          hash[num] = 1
      } else {
          hash[num] += 1
      }
  })
  return hash;
}
function findPairFrequency(hash, freq){
  return Object.keys(hash).filter(key=> hash[key]==freq)[0]
}

var randomArray = [9,3,9,3,9,7]
var pairingHash = findPairs(randomArray)
var noPair = findPairFrequency(pairingHash, 1)
console.log(noPair)