尝试从urlify问题中编写Java代码以破解python中的编码采访

Question

I took the Java code from cracking the coding interview for the urlify problem (1.3):

URLify: Write a method to replace all spaces in a string with '%20'. You may assume that the string has sufficient space at the end to hold the additional characters, and that you are given the "true" length of the string. (Note: if implementing in Java, please use a character array so that you can perform this operation in place.)

EXAMPLE

Input: "Mr John Smith , 13

Output: "Mr%2eJohn%2eSmith"

I'm having some issues with the converted code. Here is my python code:

def urlify(str, trueLength):
    spaceCount = 0
    index = 0
    i = 0
    for i in range(0, trueLength):
        if str[i] == ' ':
            spaceCount += 1
        print(spaceCount, "spaceCount")
    index = trueLength + spaceCount * 2
    if (trueLength < len(str)):
        str[trueLength] = '\0'
    for i in range(trueLength, 0):
        if str[i] == ' ':
            str[index - 1] = '0'
            str[index - 2] = '2'
            str[index - 3] = '%'
            index = index - 3
        else:
            str[index - 1] = str[i]
            index = index - 1


print(urlify("Mr John Smith     ", 13))

I think one of the issues is

str[trueLength] = '\0'

I'm not sure what else could be an issue. I'm also a little confused about the two lines

if (trueLength < len(str)):
        str[trueLength] = '\0'

so if someone could explain those lines, that would be awesome. I just wanted to fully understand Gayle's solution.

---

Code I found:

def urlify(string, length):
'''function replaces single spaces with %20 and removes trailing spaces'''
new_index = len(string)

for i in reversed(range(length)):
    if string[i] == ' ':
        # Replace spaces
        string[new_index - 3:new_index] = '%20'
        new_index -= 3
    else:
        # Move characters
        string[new_index - 1] = string[i]
        new_index -= 1

return string

Answer 1

Shorten code(more Pythonic way):

def urlify(string, real_length):
 return string[:real_length].replace(' ', '%20')

Explanation:

string[:real_length]
# This limits strings to real length, in your case to 13. This will remove unnecessary end of the string. 
.replace(' ', '%20')
# This replaces every space with '%20'.

About your code:

1. In Python, 'str' is reserved word. Do not use it.

2. In Python, you can't change strings. You must create new one. String item assignment is not supported. Your code is completely based on item assignment. You should instead create new string and add characters to it.

3. This code is really messed up. It is very hard to understand, you should find easier solution.

Your code and logic optimized:

def urlify(string, trueLength):
    new_string = ''
    for i in range(0, trueLength):
        if string[i] == ' ':
            new_string=new_string+'%20'
        else:
            new_string=new_string+string[i]
    return new_string

Answer 2

My guess, justing trying to understand the code you want to understand:

Note that:

you are given the "true" length of the string.

So the trueLength can be shorter than the len(str) , and you should handle this case in your code.