day 9 peak element

Author: mandliya

README.md

@@ -178,6 +178,7 @@ Include contains single header implementation of data structures and some algori
 | Find the missing number in Arithmetic Progression | [missingNumber2.cpp](sort_search_problems/missingNumber2.cpp) |
 | Find the common elements in 3 sorted vectors | [commonIn3Arrays.cpp](sort_search_problems/commonIn3Arrays.cpp) |
 | Find all the pairs with a given sum in an unsorted array/vector | [find_pairs_with_sum.cpp](sort_search_problems/find_pairs_with_sum.cpp) |
+| Given an array, find peak element in it. A peak element is an element that is greater than its neighbors.| [peak_element.cpp](sort_search_problems/peak_element.cpp) |
 
 ### Graph Problems
 | Problem | Solution |

sort_search_problems/peak_element.cpp

@@ -0,0 +1,50 @@
+/*
+ * Given an array, find peak element in it. A peak element is an element that is greater than its neighbors.
+ * For example,
+ *
+ * Input : [8, 9, 10, 2, 5, 6]
+ * Output: The peak element is 10
+ * Input : [8, 9, 10, 12, 15]
+ * Output: The peak element is 15
+ * Input : [10, 8, 6, 5, 3, 2]
+ * Output: The peak element is 10
+ */
+
+#include <iostream>
+
+int findPeak(int arr[], int n, int low, int high)
+{
+    // mid point
+    //
+    int mid = (low + high) / 2;
+    
+    // check if mid element is peak
+    //
+    if ((mid == 0 || arr[mid-1] <= arr[mid]) &&
+        (mid == n-1 || arr[mid+1] <= arr[mid]))
+    {
+        return mid;
+    }
+
+    // if left neighbour of mid is greater than mid element
+    // then peak would be in left array.
+    if (mid - 1 >= 0 && arr[mid-1] > arr[mid])
+    {
+        return findPeak(arr, n, low, mid-1);
+    }
+
+    // search the right side otherwise.
+    //
+    return findPeak(arr, n, mid+1, high);
+}
+
+int main()
+{
+    int arr[] = {10, 20, 30, 25, 15};
+    int n = sizeof(arr) / sizeof(arr[0]);
+
+    int peakIndex = findPeak(arr, n, 0, n-1);
+    std::cout << "The peak element of the array is:" << arr[peakIndex]
+        << std::endl;
+    return 0;
+}