RBC OA 面试真题解析：验证银行账户号码

You are in charge of creating new bank accounts when a user signs up as an RBC customer. When creating a new bank account, a valid bank account number must be provided. A valid bank account number is an integer, exactly 14 digits long, and does not contain any repeating sequence of 4 or more consecutive digits. Write a function that checks a bank account number and ensures it is valid.

Input

account_number: A string

Output

Return true or false.

Example

account_number = "hello"
valid_account_number(account_number) # Output: False

这道 RBC 面试题要求校验新开户时输入的银行账户号码。核心判断有三点：账户号必须是纯数字、长度恰好为 14 位，并且不能出现长度大于等于 4 的连续重复数字序列。实现时通常先检查字符串是否只包含数字且长度为 14，再用一次线性扫描统计连续相同数字的长度，若连续长度达到 4 就直接判定为无效。题目重点在于字符串校验与简单的线性遍历，适合用一趟扫描完成，时间复杂度为 O(n)。