Merge pull request #500 from kingdavidmartins/add.binarySearch

Add.binary search

snippets_archive/binarySearch.md

@@ -0,0 +1,24 @@
+### binarySearch
+
+Use recursion. Similar to `Array.indexOf()` that finds the index of a value within an array. 
+The difference being this operation only works with sorted arrays which offers a major performance boost due to it's logarithmic nature when compared to a linear search or `Array.indexOf()`.
+
+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 is less than the item in the middle of the interval, recurse into the lower half. Otherwise recurse into the upper half. 
+Repeatedly recurse until the value is found which is the mid or you've recursed to a point that is greater than the length which means the value doesn't exist and return `-1`.
+
+```js
+const binarySearch = (arr, val, start = 0, end = arr.length - 1) => {
+  if (start > end) return -1;
+  const mid = Math.floor((start + end) / 2);
+  if (arr[mid] > val) return binarySearch(arr, val, start, mid - 1);
+  if (arr[mid] < val) return binarySearch(arr, val, mid + 1, end);
+  return mid;
+}
+``` 
+
+```js
+binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 6); // 2
+binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 21); // -1
+```