Create 0852_Peak_Index_in_a_Mountain_Array.java

0852_Peak_Index_in_a_Mountain_Array.java

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+// id: 852
+// Name: Peak Index in a Mountain Array
+// link: https://leetcode.com/problems/peak-index-in-a-mountain-array/
+// Difficulty: Medium
+
+class Solution {
+    public int peakIndexInMountainArray(int[] arr) {
+        int peakIndex = 0;
+        int left = 0;
+        int right = arr.length - 1;
+
+        while (left < right) {
+            int mid = ( left + right ) / 2;
+
+            // check if at left peak
+            if (arr[mid] > arr[mid-1] && arr[mid] > arr[mid+1]) {
+                    peakIndex = mid;
+                    break;
+            } else if (arr[mid] > arr[mid-1]) {
+                // peak is at right
+                left = mid ;
+            } else if (arr[mid] > arr[mid+1]) {
+                right = mid ;
+            }
+        }
+
+
+        return peakIndex;
+    }
+}