Merge pull request #179 from Upendra48/recursion_questions

 Add: recursion problem:: peak in mountain array and pivot in sorted rotated array

Author: Pradeepsingh61

C++/recursion/peak_in_mountain_array.cpp

@@ -0,0 +1,26 @@
+#include <iostream>
+#include <vector>
+using namespace std;
+
+int findPeak(const vector<int>& arr, int low, int high) {
+    int mid = low + (high - low) / 2;
+    
+    // Check if mid is the peak
+    if ((mid == 0 || arr[mid] > arr[mid - 1]) && (mid == arr.size() - 1 || arr[mid] > arr[mid + 1])) {
+        return arr[mid];
+    }
+
+    // If mid is in the ascending part, move right
+    if (mid < arr.size() - 1 && arr[mid] < arr[mid + 1]) {
+        return findPeak(arr, mid + 1, high);
+    } else {
+        // Move left otherwise
+        return findPeak(arr, low, mid - 1);
+    }
+}
+
+int main() {
+    vector<int> arr = {1, 3, 8, 12, 4, 2};
+    cout << "Peak element: " << findPeak(arr, 0, arr.size() - 1) << endl;
+    return 0;
+}

C++/recursion/pivot_in_sorted_rotated_array.cpp

@@ -0,0 +1,34 @@
+#include <iostream>
+#include <vector>
+using namespace std;
+
+int findPivot(const vector<int>& arr, int low, int high) {
+    // Base case: if only one element left, it's the pivot
+    if (low == high) {
+        return low;
+    }
+    
+    int mid = low + (high - low) / 2;
+    
+    // Check if mid is the pivot
+    if (mid < high && arr[mid] > arr[mid + 1]) {
+        return mid + 1;
+    }
+    if (mid > low && arr[mid] < arr[mid - 1]) {
+        return mid;
+    }
+
+    // Decide to search in the left or right half
+    if (arr[low] >= arr[mid]) {
+        return findPivot(arr, low, mid - 1);
+    } else {
+        return findPivot(arr, mid + 1, high);
+    }
+}
+
+int main() {
+    vector<int> arr = {4, 5, 6, 7, 0, 1, 2};
+    int pivotIndex = findPivot(arr, 0, arr.size() - 1);
+    cout << "Pivot element: " << arr[pivotIndex] << " at index " << pivotIndex << endl;
+    return 0;
+}