chore(CPlusPlus): add exponential search (#352)

algorithms/CPlusPlus/README.md

@@ -33,6 +33,8 @@
 4. [Finding squareroot using Binary search](Searching/sqrt-monotonic-binary-search.cpp)
 5. [KMP String Searching](Searching/kmp.cpp)
 6. [Ternary Search](Searching/Ternary-search.cpp)
+7. [Interpolation Search](Searching/interpolation-search.cpp)
+8. [Exponential Search](Searching/exponential-search.cpp)
 
 ## Stacks
 1. [Balancing Parenthesis](Stacks/balanced-parenthesis.cpp)

algorithms/CPlusPlus/Searching/exponential-search.cpp

@@ -0,0 +1,46 @@
+/*
+Exponential search involves two steps, first to find the range within
+which the element is found and searching inside that range using
+binary search.
+*/
+
+#include <iostream>
+#include <vector>
+
+int binary_search(std::vector<int> arr, int item, int low, int high){
+	int mid;
+	while(low <= high){
+		mid = low + (high - low)/2;
+		if(arr[mid] == item){ return mid; }
+		else if(arr[mid] < item){ low = mid + 1; }
+		else{ high = mid - 1;}
+	}
+	return -1;
+}
+
+int exponential_search(std::vector<int> arr, int item){
+	int k = 1;
+	int size = arr.size() - 1;
+	while(k < size && arr[k] <= item){ k *= 2; }
+	return binary_search(arr, item, k/2, std::min(k, size));
+}
+
+int main(){
+	std::vector<int> arr;
+	for(int i=1; i<30; i+=2){ arr.push_back(i); }
+	for(int i=0; i<arr.size(); i++){ std::cout << arr[i] << " "; }
+	std::cout << std::endl;
+
+	int index = exponential_search(arr, 15);
+	std::cout << "Index of 15: " << index << std::endl;
+
+	/*
+		Output:
+		1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
+		Index of 15: 7
+
+		Time Complexity: O(log(n))
+	*/
+
+	return 0;
+}