PE004.py

#!/usr/bin/env python
# -*coding:UTF-8-*-
"""
@Project hello_world
@File PE004.py
@Author Haosen Luo
@Date 2024/12/9 7:34
"""
import numpy as np
import time

"""
最大回文乘积
回文数是指从前往后读和从后往前读都一样的数。由两个位数相乘得到的回文数中，最大的是
9009=91×99.
求最大的由两个3位数相乘得到的回文数。
"""


def timer(func):
    def inner_func(*args, **kwargs):
        begin_time = time.time()
        func(*args, **kwargs)
        print(f"Running {time.time() - begin_time} s")

    return inner_func


@timer
def main(n=2):
    min_number = 10 ** (n-1)
    max_number = 10 ** n
    array = np.arange(min_number + 1, max_number)
    two_dim_results = np.outer(array, array)
    numbers = np.ravel(two_dim_results)

    numbers.sort()
    print(numbers)

    max_palindrome = None
    # 从后往前数，返回回文数直接退出程序
    for i in range(len(numbers) - 1, -1, -1):
        s = str(numbers[i])
        if s == s[::-1]:  # 检查是否为回文数
            max_palindrome = numbers[i]
            print(max_palindrome)
            break
    print(max_palindrome)


if __name__ == '__main__':
    main(2)
    main(3)
    main(4)