852. Peak Index in a Mountain Array
Medium
An array
arr a mountain if the following properties hold:arr.length >= 3- There exists some
iwith0 < i < arr.length - 1such 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 <= 1050 <= arr[i] <= 106arris guaranteed to be a mountain array.
Runtime: 97 ms, faster than 95.21%
Memory Usage: 9.9 MB, less than 43.11%
func peakIndexInMountainArray(arr []int) int {
left := 0
right := len(arr) - 1
for left < right {
mid := ( left + right )/2
if arr[mid] < arr[mid+1] {
left = mid + 1
} else {
right = mid
}
}
return left
}
Last modified 6mo ago