function foo(nums,target)
{
    let return_arr=[];
  let mapping = {};
  for (let i =0; i <nums.length;i++)
  {
    mapping[nums[i]] = i;
  }

  for (let i =0; i <nums.length;i++)
  {
      if (nums[i] in mapping && mapping[nums[i]]>-1)
      {
        //  console.log("pushing");
          mapping[nums[i]] = -1;
          let lookfor = target - nums[i];

          if  (lookfor in mapping && mapping[lookfor]>-1){
              let lookfor_index = mapping[lookfor];
               mapping[lookfor] =-1;
               console.log("pushing: "+ i + " and " + lookfor_index);
               return_arr.push([i,lookfor_index]);
          }
      }
  }

  return return_arr;
}


//let a = foo([1, 3, 4, 5, 6, 8, 10, 11, 13],14);

//console.log(a);
// [0, 8], [1, 7], [2, 6], [4, 5]