hasPairWithSum (Google Question)

// Naive
function hasPairWithSum(arr, sum){
  var len = arr.length;
  for(var i =0; i<len-1; i++){
     for(var j = i+1;j<len; j++){
        if (arr[i] + arr[j] === sum)
            return true;
     }
  }

  return false;
}

// Better
function hasPairWithSum2(arr, sum){
  const mySet = new Set();
  const len = arr.length;
  for (let i = 0; i < len; i++){
    if (mySet.has(arr[i])) {
      return true;
    }
    mySet.add(sum - arr[i]);
  }
  return false;
}

hasPairWithSum2([6,4,3,2,1,7], 9)