[google大赛 入围赛250分真题] URLParser

Problem Statement
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When a web client (like a browser) requests a particular web page, it typically replaces certain characters with escape sequences. For instance, spaces are replaced with “%20″. Your task is to reverse this, replacing every escape sequence in the input with the character it represents. Each escape sequence is formatted as “%XX” where XX is the ASCII value of the escaped character in hexadecimal.
Definition
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Class:
URLParser
Method:
parse
Parameters:
String
Returns:
String
Method signature:
String parse(String url)
(be sure your method is public)
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Constraints
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url will contain between 1 and 50 characters, inclusive.
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Each ‘%’ in the input will be followed by a hexadecimal value between 20 (hex) and 7E (letters will be uppercase).
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Each character in the input will have ASCII value between 32 and 126, inclusive.
Examples
0)

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“http://www.%20%40%20%40%20.com/%25“
Returns: “http://www. @ @ .com/%”
“%20″ is the escape sequence for ‘ ‘, while “%40″ stands for ‘@’ and “%25″ stands for ‘%’.
1)

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“%20%21%22%23%24%25%26%27%28″
Returns: ” !\”#$%&’(“

2)

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“%48%65%6C%6C%6F%20%57%6F%72%6C%64%21″
Returns: “Hello World!”

3)

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“%2525″
Returns: “%25″

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