Lucky sevens

Write a function called lucky_sevens which takes an array of integers and returns true if any three consecutive elements sum to 7.

To solve this challenge we’ll simply loop through the array starting at the 3rd position, and checking if the number at this index plus the two previous elements sums to 7. We continue doing this as we loop through the entire array. Once we find three elements that sum to 7, we simply return true. If we reach the end of the array without finding elements that sum to 7, we return false.

function lucky_sevens(arr) {
  
  // if less than 3 elements then this challenge is not possible
  if (arr.length < 3) {
    return "not possible";
  }
  
  // because we know there are at least 3 elements we can
  // start the loop at the 3rd element in the array (i=2)
  // and check it along with the two previous elements (i-1) and (i-2)
  for (var i = 2; i < arr.length; i++) {
    if (arr[i] + arr[i-1] + arr[i-2] === 7) {
      return true; 
    }
  }
  
  // if loop is finished and no elements summed to 7
  return false;
  
}

lucky_sevens([2, 1, 5, 1, 0]);