function mus(nums){
    var nary =nums.sort();
console.log(nary);
for(var i=0; i<nums.length; i++){
       if (nums[i]==nary[i+1]){
           return true
}
       else {
           return false
}

    }
}
console.log(mus([1,1 ,3,2]));
第二種
   var  arr =[1,1,2,2,5];
var s =arr.join(',')+",";
var arrd=[];
 
console.log(s);
for (var i=0; i<arr.length; i++){
    if (s.replace(arr[i]+",","").indexOf(arr[i]+",")>-1){
        console.log(arr[i]);
arrd.push(arr[i]);
}
}
//第三種
var arr =[1,2];
arrRepeat([1,2,2,5,6])
   function arrRepeat(arr){
       var arrStr =arr.join(',')+",";
console.log(arrStr);
console
 
.log(arr);
for (var i = 0; i < arr.length; i++) {
           console.log("倒敘:"+arrStr.lastIndexOf(arr[i]));
console.log("正數:"+arrStr.indexOf(arr[i]));
if (arrStr.indexOf(arr[i]) != arrStr.lastIndexOf(arr[i])){
               return true;
}
       }
       return false;
}