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Update BinarySearch.js (#209)

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* Update BinarySearch.js

The old algorithm didn't work, I believe for two main reasons:
1 -  Number.MAX_VALUE is not a valid array index as it is used to represent the highest possible value in javascript (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_VALUE);

2 - splice() is not a pure function, every time it is called it has the side effect of modifying the original array (https://www.w3schools.com/jsref/jsref_splice.asp) ;

So I rewrote the algorithm, it now returns an index ( -1 if not found ) and it works both on numbers and on strings.

* Update BinarySearch.js

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* Update BinarySearch.js

Style change

* Update BinarySearch.js
This commit is contained in:
Askanders
2020-06-28 08:59:19 +02:00
committed by GitHub
parent 744291b7f0
commit ef5566f6a6
1 changed files with 59 additions and 15 deletions
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74
Search/BinarySearch.js
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@ -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 * 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 * 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 * to the lower half. Otherwise narrow it to the upper half. Repeatedly check until the
* value is found or the interval is empty. * value is found or the interval is empty.
*/ */
function binarySearch (arr, i) { function binarySearch (arr, x, low = 0, high = arr.length - 1) {
var mid = Math.floor(arr.length / 2) const mid = Math.floor(low + (high - low) / 2)
if (arr[mid] === i) {
console.log('match', arr[mid], i) if (high >= low) {
return arr[mid] if (arr[mid] === x) {
} else if (arr[mid] < i && arr.length > 1) { // item found => return its index
binarySearch(arr.splice(mid, Number.MAX_VALUE), i) return mid
} else if (arr[mid] > i && arr.length > 1) { }
binarySearch(arr.splice(0, mid), i)
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 { } else {
console.log('not found', i) // if low > high => we have searched the whole array without finding the item
return -1 return -1
} }
} }
var ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] /* ---------------------------------- Test ---------------------------------- */
binarySearch(ar, 3)
binarySearch(ar, 7) const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
binarySearch(ar, 13) 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'))