function permutation(arr){
  if (arr.length == 1)
    return arr;
  else if (arr.length == 2)
    return [[arr[0],arr[1]],[arr[1],arr[0]]];
  else {
    var temp = [];
    for (var i = 0; i < arr.length; i++) {
      var save = arr[i];
      arr.splice(i, 1);//取出arr[i]
      var res = permutation(arr);//递归排列arr[0],arr[1],...,arr[i-1],arr[i+1],...,arr[n]
      arr.splice(i, 0, save);//将arr[j]放入数组，保持原来的位置
      for (var j = 0; j < res.length; j++) {
        res[j].push(arr[i]);
        temp.push(res[j]);//将arr[j]组合起来
      }
    }
    return temp;
  }
}

function norepeat(contents) {
  var norepeatContents = [];
  for (var i = 0; i < contents.length; i++) {
    if(norepeatContents.indexOf(contents[i]) == -1)
      norepeatContents.push(contents[i]);
  }
  return norepeatContents;
}

function norepeat(contents) {
  var norepeatContents = [], hash = {};
  for (var i = 0; i < contents.length; i++) {
    if(!hash[contents[i]]) {
      norepeatContents.push(contents[i]);
      hash[contents[i]] = true;
    }
  }
  return norepeatContents;
}

function findMax(arr) {
  var max = arr[0];
  for (var i = 1; i < arr.length; i++) {
    if (arr[i] > max)
      max = arr[i];
  }
  return max;
}

function findMax(arr) {
  return Math.max.apply(Math, arr);
}