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Author: 10coder

PeakIndexMountainArray.java

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+//https://leetcode.com/problems/peak-index-in-a-mountain-array/
+public class PeakIndexMountainArray {
+
+    //We can traverse till end of array where we can find increasing order suddenly decreasing
+    //O(n)
+    public static int peakIndexInMountainArrayCompleteTraversal(int[] arr) {
+         int max=-1,index=0;
+        for(int i=0;i<arr.length;i++) {
+            if(arr[i]>max) {
+                max=arr[i];
+                index=i;
+            } else {
+                return index;
+            }
+        }
+         return index;
+     }
+
+    //Solving using binary Seach
+    //O(logn)
+    public static int peakIndexInMountainArrayBinarySearch(int[] arr) {
+        return mids(0,arr.length-1,arr);
+    }
+
+    public static int mids(int left, int right,int[] arr) {
+        if(left==right) {
+            return left;
+        }
+        if(left>=0 && right<arr.length) {
+            int mid=(left+right)/2;
+            if(mid+1<arr.length && arr[mid]>arr[mid+1]) {
+                if(mid-1>=0 && arr[mid]>arr[mid-1]) {
+                    return mid;
+                }
+                else {
+                    return mids(left,mid,arr);
+                }
+            } else {
+                return mids(mid,right,arr);
+            }
+        }
+        return 0;
+    }
+
+
+    public static void main(String args[]) {
+        System.out.println("Expected index 1:");
+        System.out.println(peakIndexInMountainArrayCompleteTraversal(new int[]{0,10,5,2}));
+        System.out.println(peakIndexInMountainArrayBinarySearch(new int[]{0,10,5,2}));
+    }
+}