Binary Search

Binary search is a much faster form of search. Rather than eliminating one element at a time, we eliminate half of the remaining elements at once. Works only on sorted arrays

Pseudocode.

• Accept an array and the item to search.
• initialize start (0) and end as (array.length-1). Can be called left and right as well
• While the start is less than end AND middle is not the item.
  • Find the midpoint of the array. Can use this formula. (start + (end-start))/2
  • Check if the item is before or after the midpoint.
  • If item is before midpoint, then update end to midpoint -1.
  • else if item is after midpoint, update start to midpoint +1.
  • return middle if value is found.
  • If value is not find return -1.

Time Complexity.

• Best Case is O(1).
• Average Case and Worst Case is O(log n), where n is the size of the array

Binary Search

function binarySearch(arr, value) {
  let left = 0;
  let right = arr.length - 1;
  let middle = Math.floor((left + right) / 2); //Math.floor(left +(right-left)/2)

  while (arr[middle] !== value && left <= right) {
    if (value < arr[middle]) {
      right = middle - 1;
    } else {
      left = middle + 1;
    }
    middle = Math.floor((left + right) / 2);
    // Optional middle= Math.floor(left +(right-left)/2)
  }

  return arr[middle] === value ? middle : -1;
 
}