text: // A non - empty array A consisting of N integers is given.The array contains an odd number of elements, and each element of the array can be paired with another element that has the same value, except
  // for one element that is left unpaired.
  // 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 and 2 have value 9,
  // the elements at indexes 1 and 3 have value 3,
  // the elements at indexes 4 and 6 have value 9,
  // the element at index 5 has value 7 and is unpaired.
  // Write a  function:
  
  // function solution(A);
  // that, given an array A consisting of N integers fulfilling the above conditions, returns the value of the unpaired element.
  // For example, given 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
  // function should
  // return 7, as explained in the example above.
  
  // Assume that:
  
  // N is an odd integer within the range[1. .1, 000, 000];
  // each element of array A is an integer within the range[1. .1, 000, 000, 000];
  // all but one of the values in A occur an even number of times.
  // Complexity:
  //expected worst - case time complexity is O(N);
  // expected worst - case space complexity is O(1)(not counting the storage required for input arguments).
  =================================================================== 
  
  function solution(A) {
    // write your code in JavaScript (Node.js 8.9.4)
    var result = 0;
    for (let element of A) {
      result ^= element;
    }
  
    return result;
  }
  