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JavaScript

var arr = [
  {
    "track": [
      {
        "name": "Radiapathy",
        "mbid": "4c0767f1-1c2e-4790-a8d1-ee7f78f0ac84",
        "url": "http://www.last.fm/music/The+Velvet+Teen/_/Radiapathy"
      },
      {
        "name": "How Did I Get Here",
        "mbid": "64b3078f-89cd-4ad5-bc7a-b43af082b00f",
        "url": "http://www.last.fm/music/Odesza/_/How+Did+I+Get+Here"
      },
      {
        "name": "Sunshine Roof",
        "mbid": "837db975-c93e-45ca-992c-0c924ef0f34f",
        "url": "http://www.last.fm/music/The+Innocence+Mission/_/Sunshine+Roof"
      }
    ]
  },
  {
    "track": [
      {
        "name": "Traveling",
        "mbid": "b40c24b8-3295-4219-af59-855b69958ca2",
        "url": "http://www.last.fm/music/Tennis/_/Traveling"
      },
      {
        "name": "Ghost",
        "mbid": "6273ae8f-3d2c-44c6-8c0d-53013ba79b4e",
        "url": "http://www.last.fm/music/Neutral+Milk+Hotel/_/Ghost"
      },
      {
        "name": "Strange",
        "mbid": "5a015df2-6c4a-4192-bea8-14ec5f297713",
        "url": "http://www.last.fm/music/Built+to+Spill/_/Strange"
      }
    ]
  },
  {
    "track": [
      {
        "name": "Radiapathy",
        "mbid": "4c0767f1-1c2e-4790-a8d1-ee7f78f0ac84",
        "url": "http://www.last.fm/music/The+Velvet+Teen/_/Radiapathy"
      },
      {
        "name": "Let Me Show You Love",
        "mbid": "",
        "url": "http://www.last.fm/music/Cut+Copy/_/Let+Me+Show+You+Love"
      },
      {
        "name": "Footsteps",
        "mbid": "",
        "url": "http://www.last.fm/music/Cut+Copy/_/Footsteps"
      }
    ]
  }
];

var hash = (function() {
    var keys = {};
    return {
        contains: function(key) {
            return keys[key] === true;
        },
        add: function(key) {
            if (keys[key] !== true)
            {
                keys[key] = true;
            }
        }
    };
})();

var key = null;
var noDupes = [];
var dupes = [];
for (var i = 0; i < arr.length; i++)
{
    for (var j = 0; j...