JS: find one unique value from duplicate array

index.js

/*

Given the array of IDs, which contains many duplicate integers
and one unique integer, find the unique integer.

*/

// O(n^2): loop in loop
function find_unique_brute (array) {
  var result = null, n = array.length;

  for (var i = 0; i < n; i++) {
    for (var j = i; j < n; j++) {
      if (array[i] != array[j]) {
        result = array[i];
      }
    }
  }

  return result;
}

// O(2n): loop + loop => O(n) + O(n) space
function find_unique_hash (array) {
  var n = array.length;
  var hash = {}, result = null;

  for (var i = 0; i < n; i++) {
    if (array[i] in hash) {
      hash[array[i]] += 1;
    } else {
      hash[array[i]] = 1;
    }
  }

  for (var j in hash) {
    if (hash[j] == 1) {
      result = j;
    }
  }

  return result;
}

// O(n) with no space: deep into Bits for solution
function find_unique_xor (array) {
  var result = 0, n = array.length;

  for (var i = 0; i < n; i++) {
    result ^= array[i]; 
  }

  return result;
}

var uni1 = find_unique_brute([1, 1, 5, 5, 3, 6, 6]);
var uni2 = find_unique_hash([1, 1, 5, 5, 3, 6, 6]);
var uni3 = find_unique_xor([1, 1, 5, 5, 3, 6, 6]);

console.assert(uni1 == 3, uni1 + ' should eql 3');
console.assert(uni2 == 3, uni2 + ' should eql 3');
console.assert(uni3 == 3, uni3 + ' should eql 3');

console.log('all passed');