/* Binary Search-Search a sorted array by repeatedly dividing the search interval
 * in half. Begin with an interval covering the whole array. If the value of the
 * search key is less than the item in the middle of the interval, narrow the interval
 * to the lower half. Otherwise narrow it to the upper half. Repeatedly check until the
 * value is found or the interval is empty.
 */

function binarySearch (arr, i) {
  var mid = Math.floor(arr.length / 2)
  if (arr[mid] === i) {
    console.log('match', arr[mid], i)
    return arr[mid]
  } else if (arr[mid] < i && arr.length > 1) {
    binarySearch(arr.splice(mid, Number.MAX_VALUE), i)
  } else if (arr[mid] > i && arr.length > 1) {
    binarySearch(arr.splice(0, mid), i)
  } else {
    console.log('not found', i)
    return -1
  }
}

var ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
binarySearch(ar, 3)
binarySearch(ar, 7)
binarySearch(ar, 13)