[Solved] An array arr a mountain if the following properties hold: arr.length >= 3, There exists some i with 0 < i < arr.length - 1 such that:

Question

An array arr a mountain if the following properties hold:

  • arr.length >= 3
  • There exists some i with 0 < i < arr.length - 1 such that:
    • arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
    • arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

Given a mountain array arr, return the index i such that arr[0] < arr[1] < ... < arr[i - 1] < arr[i] > arr[i + 1] > ... > arr[arr.length - 1].

You must solve it in O(log(arr.length)) time complexity.

Example 1:

Input: arr = [0,1,0]
Output: 1

Example 2:

Input: arr = [0,2,1,0]
Output: 1

Example 3:

Input: arr = [0,10,5,2]
Output: 1

Constraints:

  • 3 <= arr.length <= 105
  • 0 <= arr[i] <= 106
  • arr is guaranteed to be a mountain array.

Python Solution

class Solution:
    def peakIndexInMountainArray(self, A: List[int]) -> int:
        l=0
        r=len(A)-1
        mx=0

        while l<=r:
            m = l+(r-l)//2

            if A[m-1]<A[m] and A[m+1]<A[m]:
                return (m)
            elif A[m-1]<=A[m] and A[m+1]>=A[m]:
                l=m+1
            else:
                r=m-1
Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

Articles: 514

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