给定两个数组，写一个方法来计算它们的交集。

 function intersection(arr1,arr2){
        var arr=[]
        arr2.forEach(arr2Item=>{
            var index=arr1.indexOf(arr2Item);
            if(index!=-1){
                arr.push(arr2Item);
                arr1.splice(index,1);
            }
        })
      return arr;
    }

  function intersection(arr1,arr2){
        var arr=[]
        arr1=arr1.sort((x,y)=>x-y);
        arr2=arr2.sort((x,y)=>x-y);
        var i=0;
        var j=0;
        while(i<arr1.length&&j<arr2.length){
            if(arr1[i]<arr2[j]){
                i++;
            }else if(arr1[i]==arr2[j]){
                arr.push(arr1[i])
                i++;
                j++;
            }else{
                j++
            }
        }
      return arr;
    }

 function toMap(arr){
        var mapArr=new Map();
        for(let i=0;i<arr.length;i++){
            let num=mapArr.get(arr[i]);
            mapArr.set(arr[i],num?num+1:1);
        }
        return mapArr;
    }
    function intersection(arr1,arr2){
        var arr=[]
       var  mapArr1=toMap(arr1);
       var  mapArr2=toMap(arr2);
        mapArr1.forEach((arr1Item,key)=>{
            var arr1ItemCount=arr1Item;
            var arr2ItemConnt=mapArr2.get(key);
            if(arr1ItemCount&&arr2ItemConnt){
                var maxCount=Math.min(arr1ItemCount,arr2ItemConnt)
                while(maxCount--){
                    arr.push(key);
                }
            }
        })
      return arr;
    }