852_Peak_Index_in_a_Mountain_Array

Author: qiyuangong

README.md

@@ -168,6 +168,7 @@ Also, there are open source implementations for basic data structs and algorithm
 | 811 | [Subdomain Visit Count](https://leetcode.com/problems/subdomain-visit-count/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/811_Subdomain_Visit_Count.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/811_Subdomain_Visit_Count.java) | String split and HashMap, O(n) and O(n) |
 | 819 | [Most Common Word](https://leetcode.com/problems/most-common-word/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/819_Most_Common_Word.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/819_Most_Common_Word.java) | String processing, be careful about 'b,b,b'. regex is recommended. |
 | 844 | [Backspace String Compare](https://leetcode.com/problems/backspace-string-compare/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/844_Backspace_String_Compare.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/844_Backspace_String_Compare.java) | 1. Stack pop when encounters #, O(n) and O(n)<br>2. Compare string from end to start, O(n) and O(1) |
+| 852 | [Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/852_Peak_Index_in_a_Mountain_Array.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/852_Peak_Index_in_a_Mountain_Array.java) | 1. Scan the array until encountering decline, O(n) and O(1)<br>2. Binary seach with additional check for [i + 1], O(logn) and O(1)|
 | 904 | [Fruit Into Baskets](https://leetcode.com/problems/fruit-into-baskets/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/904_Fruit_Into_Baskets.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/904_Fruit_Into_Baskets.java) | 1. Scan through blocks of tree, O(n) and O(n)<br>2. Mainten a sliding window with start and curr point, O(n) and O(n).  |
 | 922 | [Sort Array By Parity II](https://leetcode.com/problems/sort-array-by-parity-ii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/922_Sort_Array_By_Parity_II.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/922_Sort_Array_By_Parity_II.java) | 1. Place odd and even number in odd and even place, not sort is needed. O(n) and O(1)<br>2. Two points with quick sort swap idea, O(n) and O(1). |
 | 929 | [Unique Email Addresses](https://leetcode.com/problems/unique-email-addresses/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/929_Unique_Email_Addresses.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/929_Unique_Email_Addresses.java) | String handle and hash (or set) |

java/852_Peak_Index_in_a_Mountain_Array.java

@@ -0,0 +1,17 @@
+class Solution {
+    // public int peakIndexInMountainArray(int[] A) {
+    //     int i = 0;
+    //     for (; A[i] < A[i + 1]; i++);
+    //     return i;
+    // }
+
+    public int peakIndexInMountainArray(int[] A) {
+        int lo = 0, hi = A.length - 1;
+        while (lo < hi) {
+            int mid = (lo + hi) / 2;
+            if (A[mid] < A[mid + 1]) lo = mid + 1;
+            else hi = mid;
+        }
+        return lo;
+    }
+}

python/852_Peak_Index_in_a_Mountain_Array.py

@@ -0,0 +1,20 @@
+class Solution(object):
+    # def peakIndexInMountainArray(self, A):
+    #     """
+    #     :type A: List[int]
+    #     :rtype: int
+    #     """
+    #     i = 0
+    #     while A[i + 1] >= A[i]:
+    #         i += 1
+    #     return i
+
+    def peakIndexInMountainArray(self, A):
+        lo, hi = 0, len(A) - 1
+        while lo < hi:
+            mid = (lo + hi) / 2
+            if A[mid] < A[mid + 1]:
+                lo = mid + 1
+            else:
+                hi = mid
+        return lo