1064. Fixed Point

class Solution:
    def fixedPoint(self, arr: List[int]) -> int:
        left, right = 0, len(arr) - 1
        while left < right:
            mid = (left + right) >> 1
            if arr[mid] >= mid:
                right = mid
            else:
                left = mid + 1
        return left if arr[left] == left else -1