peak-index-in-a-mountain-array.go

// 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.
//
//


func peakIndexInMountainArray(A []int) int {
    low, high := 0, len(A)-1
    for low < high {
        middle := (low+high)/2
        if A[middle] < A[middle+1] {
            low = middle +1
        } else {
            high = middle
        }
    }
    return low
}