如何检查最大可能的回文整数

Question

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。该函数返回最大可能的回文整数可以通过将输入数字的最多 k 位更改为 0-9 的任何其他数字来找到。

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）。如果我们进行三个更改，我们将得到 1921 到 9999，这是可能的最高四位数整数值。

我相信我使用的代码会检查数字是否为回文，但并没有给出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。

Answer 1

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 是整数而非字符串