写个二分查找吧~

def bi_search(arr, t):
	if not arr or t < arr[0] or t > arr[-1]:  # 边界情形
		return None
	begin, end = 0, len(arr) - 1
	while begin <= end:
		mid = begin + (end - begin) // 2  # 防止大数相加溢出
		if t == arr[mid]:
			return mid
		elif t < arr[mid]:
			end = mid - 1
		elif t > arr[mid]:
			begin = mid + 1
	return None

arr1 = [1, 2, 2, 4, 5, 7, 7, 8, 9, 9, 10]
arr2 = [2]
arr3 = [2, 2]
arr4 = []  # 不能进行索引
for arr in [arr1, arr2, arr3, arr4]:
	print(bi_search(arr, 10))

区间思维