find peak element medium

Author: weiy

Array/FindPeakElement.py

@@ -0,0 +1,55 @@
+"""
+A peak element is an element that is greater than its neighbors.
+
+Given an input array nums, where nums[i] ≠ nums[i+1], find a peak element and return its index.
+
+The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.
+
+You may imagine that nums[-1] = nums[n] = -∞.
+
+Example 1:
+
+Input: nums = [1,2,3,1]
+Output: 2
+Explanation: 3 is a peak element and your function should return the index number 2.
+Example 2:
+
+Input: nums = [1,2,1,3,5,6,4]
+Output: 1 or 5 
+Explanation: Your function can return either index number 1 where the peak element is 2, 
+             or index number 5 where the peak element is 6.
+Note:
+
+Your solution should be in logarithmic complexity.
+
+log n待续。
+
+先O(n)。
+
+看来测试数据不多，O(n) 的可以 beat 100%.
+
+测试地址：
+https://leetcode.com/problems/find-peak-element/description/
+
+"""
+class Solution(object):
+    def findPeakElement(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        
+        length = len(nums)
+        
+        for i in range(1, length-1):
+            if nums[i-1] < nums[i] > nums[i+1]:
+                return i
+        
+        if length <= 2:
+            return nums.index(max(nums))
+        else:
+            if nums[0] > nums[1]:
+                return 0
+            elif nums[-1] > nums[-2]:
+                return length-1
+            return None