gistfile1.js

function solve(src) {
  var _src = src.split('<script>');
  var text = _src[1] && _src[1].match(/\[[^\]]+\]/);
  if (!text) return console.log(src);
  var list = JSON.parse(text);
  var answer = new Array(list.length);
  list.forEach(function(item, i){
    if (answer[i]) return;
    var f = list.indexOf(item, i+1);
    if (f !== -1) {
      answer[i] = f;
      answer[f] = i;
    }
  });
  var form=document.getElementById('solve');
  var x = new XMLHttpRequest();
  x.open(form.method, form.action, true);
  x.onload = function(){
    setTimeout(function(){
      solve(x.responseText);
    }, 1000);
  };
  x.onerror = function(){
    console.log(x);
  };
  x.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  x.send('answer='+answer.join(','));
}

solve(document.documentElement.innerHTML);