And I did it by myself. I had an algorithm in mind to start with, but when it failed, I just… did trial and error most of the way forward - of course with some thought.

```
function pairwise(arr, arg) {
var sum = 0;
var used = [];
for(var i = 0; i < arr.length-1; i++){
for(var j = i+1; j < arr.length; j++){
if(arr[i] + arr[j] == arg){
if(used.includes(i) || used.includes(j, j)){
continue;
} else {
sum += (i+j);
used.push(i, j);
i++;
j++;
}
}
}
}
return sum;
}
pairwise([0,0,0,0,1,1], 1);
```