Update BinarySearch.js

Search/BinarySearch.js

@@ -1,26 +1,70 @@
-/* Binary Search-Search a sorted array by repeatedly dividing the search interval
+/* Binary Search: https://en.wikipedia.org/wiki/Binary_search_algorithm
+ *
+ * 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)
+function binarySearch (arr, x, low = 0, high = arr.length - 1) {
+ const mid = Math.floor(low + (high - low) / 2)
+
+ if (high >= low) {
+ if (arr[mid] === x) {
+ // item found => return its index
+ return mid
+ }
+
+ if (x < arr[mid]) {
+ // arr[mid] is an upper bound for x, so if x is in arr => low <= x < mid
+ return binarySearch(arr, x, low, mid - 1)
+ } else {
+ // arr[mid] is a lower bound for x, so if x is in arr => mid < x <= high
+ return binarySearch(arr, x, mid + 1, high)
+ }
  } else {
- console.log('not found', i)
+ // if low > high => we have searched the whole array without finding the item
  return -1
  }
 }
 
-var ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
-binarySearch(ar, 3)
-binarySearch(ar, 7)
-binarySearch(ar, 13)
+/* ---------------------------------- Test ---------------------------------- */
+
+const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+const stringArr = [
+ 'Alpha',
+ 'Bravo',
+ 'Charlie',
+ 'Delta',
+ 'Echo',
+ 'Foxtrot',
+ 'Golf',
+ 'Hotel',
+ 'India',
+ 'Juliet',
+ 'Kilo',
+ 'Lima',
+ 'Mike',
+ 'November',
+ 'Oscar',
+ 'Papa',
+ 'Quebec',
+ 'Romeo',
+ 'Sierra',
+ 'Tango',
+ 'Uniform',
+ 'Victor',
+ 'Whiskey',
+ 'X-Ray',
+ 'Yankee',
+ 'Zulu'
+]
+
+console.log(binarySearch(arr, 3))
+console.log(binarySearch(arr, 7))
+console.log(binarySearch(arr, 13))
+
+console.log(binarySearch(stringArr, 'Charlie'))
+console.log(binarySearch(stringArr, 'Zulu'))
+console.log(binarySearch(stringArr, 'Sierra'))