[Search] Add a solution to Peak Index in a Mountain Array, update the…

… solution to Find Peak Element

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 264 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 265 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -306,6 +306,7 @@
 [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/)| [Swift](./Search/Search2DMatrixII.swift)| Medium| O(m + n)| O(1)|
 [Search for a Range](https://leetcode.com/problems/search-for-a-range/)| [Swift](./Search/SearchForARange.swift)| Medium| O(logn)| O(1)|
 [Search Insert Position](https://leetcode.com/problems/search-insert-position/)| [Swift](./Search/SearchForARange.swift)| Medium| O(logn)| O(1)|
+[Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/)| [Swift](./Search/PeakIndexMountainArray.swift)| Easy| O(logn)| O(1)|
 [Find Peak Element](https://leetcode.com/problems/find-peak-element/)| [Swift](./Search/FindPeakElement.swift)| Medium| O(logn)| O(1)|
 [Sqrt(x)](https://leetcode.com/problems/sqrtx/)| [Swift](./Search/Sqrtx.swift)| Medium| O(logn)| O(1)|
 [Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)| [Swift](./Search/MedianTwoSortedArrays.swift)| Hard| O(log(m + n))| O(1)|

Search/FindPeakElement.swift

@@ -6,30 +6,19 @@
  */
 
 class FindPeakElement {
-    func findPeakElement(nums: [Int]) -> Int {
-        guard nums.count > 1 else {
-            return 0
-        }
-
-        var left = 1
-        var right = nums.count - 2
-        var mid = 0
+    func findPeakElement(_ nums: [Int]) -> Int {
+        var left = 0, right = nums.count - 1, mid = 0
 
-        while left <= right {
+        while left < right {
             mid = (right - left) / 2 + left
-            if nums[mid] > nums[mid - 1] && nums[mid] > nums[mid + 1] {
-                return mid
-            } else if nums[mid] < nums[mid + 1] {
-                left = mid + 1
+
+            if nums[mid] > nums[mid + 1] {
+                right = mid
             } else {
-                right = mid - 1
+                left = mid + 1
             }
         }
 
-        if nums[left] >= nums[right] {
-            return left
-        } else {
-            return right
-        }
+        return left
     }
 }

Search/PeakIndexMountainArray.swift

@@ -0,0 +1,25 @@
+/**
+ * Question Link: https://leetcode.com/problems/peak-index-in-a-mountain-array/
+ * Primary idea: Classic Binary Search  
+ *
+ * Time Complexity: O(logn), Space Complexity: O(1)
+ */
+
+
+class PeakIndexMountainArray {
+    func peakIndexInMountainArray(_ A: [Int]) -> Int {
+        var left = 0, right = A.count - 1, mid = 0
+
+        while left < right {
+            mid = (right - left) / 2 + left
+
+            if A[mid] > A[mid + 1] {
+                right = mid
+            } else {
+                left = mid + 1
+            }
+        }
+
+        return left
+    }
+}