Add binary search template

Author: jinshendan

Template/Maths/Binary-Search/Binary-Search.cpp

@@ -0,0 +1,19 @@
+// An example of binary search.
+// Return the index if the target value could be found in the array, otherwise, return -1;
+
+int binary_search(vector<int> arr, int target) {
+    int left = 0, right = arr.size() - 1;
+    while(left <= right) {
+        int mid = (right - left) / 2 + left;
+        if (arr[mid] == target)  {
+            return mid;
+        }
+        else if (arr[mid] > target){
+            right = mid - 1;
+        }
+        else if (arr[mid] < target){
+            left = mid + 1;
+        }
+    }
+    return -1;
+}