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python - 如何检查最大可能的回文整数

问题描述

我正在处理一个要求我使用函数的赋值，该函数带有两个参数：一个字符串形式的整数，例如 '1921'，以及一个整数 k，例如 2。该函数返回一个可以找到的最大可能的回文整数通过将输入数字的最多 k 位更改为 0-9 的任何其他数字。

例如，最多对 1921 进行两次更改，最大可能的回文数是 1991（一次更改 2 -> 9）。如果我们进行三处更改，我们将得到 1921 到 9999，这是可能的最高四位数整数值。

我相信我正在使用的代码检查数字是否是回文，但并没有给我我能得到的最大可能的回文。

使用的代码：

def Is_palindrome(str):
    x = 0 
    for i in range (len(str)/2):
        if (str[x]) == (word[len(str)-x-1]):
            x+=1
        if x == (len(str)/2):
            return True
    return False

def longest_palindrome(str):
    lst = str.split() 
    palindromes = [] #List that contains the palindromes
    long_len = 0 #Length of the longest palindrome
    longest = "" #The actual longest palindrome
    for i in lst: 
        if Is_palindrome(i): #If the str is a palindrome
            palindromes.append(i) #Add it to the palindrome list
    for i in palindromes: #Loop through the palindrome list
        if len(i) > long_len: #If the palindrome is longer than the 
longest one
            longest = i #Set it as the longest one
            longest_len = len(i) # Set the length of the longest one to 
the length of this one
    return longest

如果您有任何建议，请告诉我！！提前致谢。

标签： pythonpalindrome

解决方案

请尝试以下代码：

import sys

def maximumPalinUsingKChanges(str, k):
    palin = []

    a = 0
    b = len(str)

    while (a < b):
        palin.append(str[a])
        a = a + 1

    # Iinitialize l and r by leftmost and
    # rightmost ends
    l = 0
    r = len(str) - 1

    #  first try to make string palindrome
    while (l < r):
        # Replace left and right character by
        # maximum of both
        if (str[l] != str[r]):
            palin[l] = max(str[l], str[r])
            palin[r] = max(str[l], str[r])
            k = k - 1
        l = l + 1
        r = r - 1    

    # If k is negative then we can't make
    # string palindrome
    if (k < 0):
        print("Not possible")
        return "Not possible"

    l = 0
    r = len(str) - 1

    while (l <= r):
        # At mid character, if K>0 then change
        # it to 9
        if (l == r):
            if (k > 0):
                palin[l] = '9'

        # If character at lth (same as rth) is
        # less than 9
        if (palin[l] < '9'):
            #If none of them is changed in the
            #  previous loop then subtract 2 from K
            # and convert both to 9 
            if (k >= 2 and palin[l] == str[l] and palin[r] == str[r]):
                k -= 2
                palin[l] = '9'
                palin[r] = '9'

            #  If one of them is changed in the previous
            #  loop then subtract 1 from K (1 more is
            #  subtracted already) and make them 9  
            elif (k >= 1 and (palin[l] != str[l] or palin[r] != str[r])):
                k = k - 1
                palin[l] = '9'
                palin[r] = '9'

        l = l + 1
        r = r - 1

    print(''.join(palin))
    return ''.join(palin)

确保 k 是整数而不是字符串

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