SOURCE

function solve(arr,sum){
    let i=0
    let j=arr.length-1
    let first,last
    while(i<j){
        first=arr[i]
        last=arr[j]
        const tog=first+last
        console.log(tog)
        if(tog===sum){
            return [first,last]
        }
        else if(tog>sum) {j--}
        else {i++}
    }
    return null
}
console.log(solve([1,2,3,4,5],4))