[LeetCode] Problem 852 - Peak Index in a Mountain Array

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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

No.1

Input: [0,1,0]

Output: 1

No.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.

Code

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public int peakIndexInMountainArray(int[] A) {
    int left = 0;
    int right = A.length - 1;

    while (left < right) {
        int mid = (left + right) >> 1;
        
        if (A[mid] < A[mid + 1])
            left = mid + 1;
        else
            right = mid;
    }

    return left;
}