Python Challenges: Find the largest palindrome made from the product of two 4-digit numbers

Last update on May 28 2022 13:42:30 (UTC/GMT +8 hours)

Python Challenges - 1: Exercise-36 with Solution

Write a Python program to find the largest palindrome made from the product of two 4-digit numbers.

According Wikipedia - A palindromic number or numeral palindrome is a number that remains the same when its digits are reversed. Like 16461, for example, it is "symmetrical". The term palindromic is derived from palindrome, which refers to a word (such as rotor or racecar) whose spelling is unchanged when its letters are reversed. The first 30 palindromic numbers (in decimal) are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 202, …

The largest palindrome made from the product of two 3-digit numbers is 913 * 993 = 906609.
Note: 9999 * 9901 = 906609

Sample Solution:-

Python Code:

n = 0
for a in range(9999, 100, -1):
    for b in range(a, 100, -1):
        x = a * b
        if x > n:
            s = str(a * b)
            if s == s[::-1]:
                n = a * b
print(n)

Sample Output:

99000099

Flowchart:

Python Code Editor:

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Next: Write a Python program to find the smallest positive number that is evenly divisible by all of the numbers from 1 to 30.

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

The os and os.path modules.
The __file__ constant
os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
os.path.dirname(path) (returns "the directory name of pathname path")
os.getcwd() (returns "a string representing the current working directory")
os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m