add 852

Author: fishercoder1534

README.md

@@ -34,6 +34,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |900|[Sort Array By Parity](https://leetcode.com/problems/sort-array-by-parity/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_900.java) | O(n) | O(1) | |Easy|
 |896|[Monotonic Array](https://leetcode.com/problems/monotonic-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_896.java) | O(n) | O(1) | |Easy|
 |884|[Uncommon Words from Two Sentences](https://leetcode.com/problems/uncommon-words-from-two-sentences/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_884.java) | O(n) | O(k) | |Easy|
+|852|[Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_852.java) | O(n) | O(1) | |Easy|
 |844|[Backspace String Compare](https://leetcode.com/problems/backspace-string-compare/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_844.java) | O(n) | O(1) | |Easy|
 |832|[Flipping an Image](https://leetcode.com/problems/flipping-an-image/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_832.java) | O(n) | O(1) | |Easy|
 |830|[Positions of Large Groups](https://leetcode.com/problems/positions-of-large-groups/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_830.java) | O(n) | O(n) | |Easy|

src/main/java/com/fishercoder/solutions/_852.java

@@ -0,0 +1,35 @@
+package com.fishercoder.solutions;
+
+/**852. Peak Index in a Mountain Array
+ *
+ * Let's call an array A a mountain if the following properties hold:
+ *
+ * A.length >= 3
+ * There exists some 0 < i < A.length - 1 such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]
+ * Given an array that is definitely a mountain, return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].
+ *
+ * Example 1:
+ *
+ * Input: [0,1,0]
+ * Output: 1
+ * Example 2:
+ *
+ * Input: [0,2,1,0]
+ * Output: 1
+ * Note:
+ *
+ * 3 <= A.length <= 10000
+ * 0 <= A[i] <= 10^6
+ * A is a mountain, as defined above.*/
+public class _852 {
+    public static class Solution1 {
+        public int peakIndexInMountainArray(int[] A) {
+            for (int i = 1; i < A.length - 1; i++) {
+                if (A[i] > A[i+1]) {
+                    return i;
+                }
+            }
+            return 0;
+        }
+    }
+}

src/test/java/com/fishercoder/_852Test.java

@@ -0,0 +1,29 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._852;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class _852Test {
+    private static _852.Solution1 solution1;
+    private static int[] A;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _852.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        A = new int[]{0, 1, 0};
+        assertEquals(1, solution1.peakIndexInMountainArray(A));
+    }
+
+    @Test
+    public void test2() {
+        A = new int[]{0, 2, 1, 0};
+        assertEquals(1, solution1.peakIndexInMountainArray(A));
+    }
+}