刷題日記（8）Find Peak Element

A peak element is an element that is strictly greater than its neighbors.

Given an integer array nums, find a peak element, and return its index. If the array contains multiple peaks, return the index to any of the peaks.

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: 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.

Constraints:

• 1 <= nums.length <= 1000 (所以list不為null)
• -231 <= nums[i] <= 231 - 1
• nums[i] != nums[i + 1] for all valid i.( 鄰近的兩個數一定不一樣)

Follow up: Could you implement a solution with logarithmic complexity?

peak的可能只有三種case

以這個作為例子

solution中很聰明的解法，只要比較i和後面一個的位置，i+1比較小的話就能確定是peak了

這個解法時間複雜度是n