Create 1095_Find_in_Mountain_Array.java

1095_Find_in_Mountain_Array.java

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+// id: 1095
+// Name: Find in Mountain Array
+// link: https://leetcode.com/problems/find-in-mountain-array/
+// Difficulty: Hard
+
+/**
+ * // This is MountainArray's API interface.
+ * // You should not implement it, or speculate about its implementation
+ * interface MountainArray {
+ *     public int get(int index) {}
+ *     public int length() {}
+ * }
+ */
+
+class Solution {
+
+    private boolean isAscending = true;
+
+    private boolean shouldGoRight(int current, int target) {
+        if (isAscending) {
+            return current < target;
+        } else {
+            return current > target;
+        }
+    }
+
+
+    public int findInMountainArray(int target, MountainArray mountainArr) {
+        int peakIndex = 0;
+        int left = 0;
+        int right = mountainArr.length() - 1;
+
+        while (left < right) {
+            int mid = ( left + right ) / 2;
+
+            int current = mountainArr.get(mid);
+            int leftOfMid = mountainArr.get(mid-1);
+            int rightOfMid = mountainArr.get(mid+1);
+
+
+            // check if at left peak
+            if (current > leftOfMid && current > rightOfMid) {
+                peakIndex = mid;
+                break;
+            } else if (current > leftOfMid) {
+                // peak is at right
+                left = mid ;
+            } else if (current > rightOfMid) {
+                right = mid ;
+            }
+        }
+
+        int result = binarySearch(target, mountainArr, 0, peakIndex);
+
+        isAscending = false;
+
+        if (result == -1) {
+            result = binarySearch(target, mountainArr, peakIndex, mountainArr.length()-1);
+        }
+
+        return result;
+    }
+
+
+    // both start, and end, inclusive
+    private int binarySearch(int target, MountainArray mountainArr, int start, int end) {
+        while (start <= end) {
+            int mid = (start + end) / 2;
+            int current = mountainArr.get(mid);
+
+            if (current == target) {
+                return mid;
+            } else if (shouldGoRight(current, target)) {
+                start = mid + 1;
+            } else {
+                end = mid - 1;
+            }
+        }
+        return -1;
+    }
+}