Merge pull request deutranium#100 from ankur-kayal/exponential-search

Exponential Search in C++ Added

Author: deutranium

searchingAlgo/exponentialSearch/README.md

@@ -1,40 +1,60 @@
-
 # Exponential Search
 
- - Exponential search allows for searching through a sorted, unbounded list for a specified input value.
- - Time Complexity:
-	 - Worst Case Complexity:_O_(log _i_)
-	 - Best Case Complexity:_O_(1)
-	 - Average Case Complexity:_O_(log _i_)
+- Exponential search allows for searching through a sorted, unbounded list for a specified input value.
+- Time Complexity:
+  - Worst Case Complexity:_O_(log _i_)
+  - Best Case Complexity:_O_(1)
+  - Average Case Complexity:_O_(log _i_)
 - Worst Case Space Complexity:_O_(1)
-- Exponential Search will run in  _O_(log _i_) time, where  _i_  is the index of the element being searched for in the list, whereas binary search would run in  _O_(log _n_) time, where  _n_  is the number of elements in the list.
+- Exponential Search will run in _O_(log _i_) time, where _i_ is the index of the element being searched for in the list, whereas binary search would run in _O_(log _n_) time, where _n_ is the number of elements in the list.
 - Works only on sorted lists.
 
 ### Logic
 
- 1.  Find range where element is present
+1.  Find range where element is present
 2.  Do Binary Search in above found range.
- 3. Pseudo Code:	
+3.  Pseudo Code:
+
+           function exponentialSearch(arr, x, lo, hi):
+        	if arr[hi] >= x:
+        		return(binarySearch(arr, x, lo, hi + 1))
+        	else:
+        		return(exponentialSearch(arr, x, hi, hi * 2))
+
+        	function binarySearch(arr, x, lo, hi):
+        		index = (lo + hi)/2
+        		if x = arr[index]
+        			return index
+        		else if x > arr[index]:
+        			return binarySearch(arr, x, index, hi)
+        		else:
+        			return binarySearch(arr, x, 0, index)
 
-		   function exponentialSearch(arr, x, lo, hi):
-			if arr[hi] >= x:
-				return(binarySearch(arr, x, lo, hi + 1))
-			else:
-				return(exponentialSearch(arr, x, hi, hi * 2))
+### Implementations
 
-			function binarySearch(arr, x, lo, hi):
-				index = (lo + hi)/2
-				if x = arr[index]
-					return index
-				else if x > arr[index]:
-					return binarySearch(arr, x, index, hi)
-				else:
-					return binarySearch(arr, x, 0, index)
+- [Python](exponentialSearch.py)
+- [C++](exponentialSearch.cpp)
 
-###  Instruction for Running code:
+### Instruction for Running code:
 
 - Python
 
 ```
 python3 exponentialSearch.py
 ```
+
+- C++
+
+For Windows
+
+```
+g++ exponentialSearch.cpp -o exponentialSearch.exe
+exponentialSearch.exe
+```
+
+For Linux/ Mac
+
+```
+g++ exponentialSearch.cpp -o exponentialSearch.out
+./exponentialSearch.out
+```

searchingAlgo/exponentialSearch/exponentialSearch.cpp

@@ -0,0 +1,56 @@
+#include <bits/stdc++.h> 
+using namespace std; 
+
+// A recursive binary search function. It returns location of x in given array a[l..r] is  present, otherwise -1 
+int binarySearch(vector<int> &a, int l, int r, int x)  { 
+	if (r >= l) { 
+		int mid = l + (r - l)/2; 
+
+		// If the element is present at the middle itself 
+		if (a[mid] == x) 
+			return mid; 
+
+		// If element is smaller than mid, then it can only be present in left subarray 
+		if (a[mid] > x) 
+			return binarySearch(a, l, mid-1, x); 
+
+		// Else the element can only be present in right subarray 
+		return binarySearch(a, mid+1, r, x); 
+	} 
+
+	// We reach here when element is not present in array 
+	return -1; 
+} 
+
+// Returns position of first occurrence of x in array 
+int exponentialSearch(vector<int> &a, int n, int x) { 
+	// If x is present at firt location itself 
+	if (a[0] == x) 
+		return 0; 
+
+	// Find range for binary search by 
+	// repeated doubling 
+	int i = 1; 
+	while (i < n && a[i] <= x) 
+		i = i<<1; 
+
+	// Call binary search for the found range. 
+	return binarySearch(a, i/2, min(i, n), x); 
+} 
+
+
+
+
+// Driver code 
+int main()  { 
+	vector<int> a = {2, 5, 6, 7, 9, 15, 23, 24, 89}; 
+	int n = a.size(); 
+	int x = 15; 
+	int result = exponentialSearch(a, n, x); 
+	if(result != -1) {
+		cout << "\nElement found at index: " << result << '\n';
+	}
+	else {
+		cout << "\nElement not found!\n";
+	}
+}