数字2出现的次数。python

可以使用引用中的方法来统计数字2在给定列表中出现的次数。具体实现方法如下：

def count_num(lst, num):
    left = 0
    right = len(lst) - 1
    left_idx = get_left_idx(lst, num, left, right)
    right_idx = get_right_idx(lst, num, left, right)
    if left_idx == -1 or right_idx == -1:
        return 0
    return right_idx - left_idx + 1

def get_left_idx(lst, num, left, right):
    while left <= right:
        mid = (left + right) // 2
        if lst[mid] < num:
            left = mid + 1
        else:
            right = mid - 1
    if left < len(lst) and lst[left] == num:
        return left
    else:
        return -1

def get_right_idx(lst, num, left, right):
    while left <= right:
        mid = (left + right) // 2
        if lst[mid] <= num:
            left = mid + 1
        else:
            right = mid - 1
    if right >= 0 and lst[right] == num:
        return right
    else:
        return -1

lst = [1, 2, 2, 3, 4, 5, 6, 7, 8, 9, 10]
num = 2
count = count_num(lst, num)
print("数字2在列表中出现的次数为：", count)

输出结果为：数字2在列表中出现的次数为： 2。