# [LeetCode]#852. Peak Index in a Mountain Array

**Environment: Python 3.7**

**Key technique:** index.max() function

Let’s call an array `A`

a *mountain* if the following properties hold:

`A.length >= 3`

- There exists some
`0 < i < A.length - 1`

such that`A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]`

Given an array that is definitely a mountain, return any `i`

such that `A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]`

.

**Example 1:**

**Input: **[0,1,0]

**Output: **1

**Example 2:**

**Input: **[0,2,1,0]

**Output: **1

**Note:**

`3 <= A.length <= 10000`

`0 <= A[i] <= 10^6`

- A is a mountain, as defined above.

**Analysis:**

Assume peak is maximum value in list and use index.max() function to find location.

**Solution:**

`class Solution:`

def peakIndexInMountainArray(self, A):

ans=A.index(max(A))

return ans

**Submitted result:**

**Reference:**