852. Peak Index in a Mountain Array

852. Peak Index in a Mountain Array

這個題目是 162. Find Peak Element 的精簡版。

1. 在閉區間搜尋
2. 從中間開始找
   1. 如果下一個數字比現在的大，向右逼近
   2. 如果下一個數字比現在小或是一樣，向左逼近

class Solution:
    def peakIndexInMountainArray(self, arr: List[int]) -> int:
        left = 0
        right = len(arr) - 1

        while left < right:
            mid = left + (right - left) // 2
            # Peak is on right hand side
            if arr[mid] < arr[mid + 1]:
                left = mid + 1
            # Peak is on left hand side. Or mid is the peak
            else: # arr[mid] >= arr[mid + 1]
                right = mid
        
        return left