[C++]Google Code Jam中国竞赛原题解析[一]

Problem Statement

      You are given a string input. You are to find the longest substring of input such that the reversal of the substring is also a substring of input. In case of a tie, return the string that occurs earliest in input.

Definition

      Class:  ReverseSubstring  
Method:  findReversed  
Parameters:  string  
Returns:  string  
Method signature:  string findReversed(string input)  
(be sure your method is public)  
      
 

Notes

-  The substring and its reversal may overlap partially or completely.  
-  The entire original string is itself a valid substring (see example 4).  

Constraints

-  input will contain between 1 and 50 characters, inclusive.  
-  Each character of input will be an uppercase letter ('A'-'Z').  

Examples

0)   
      "XBCDEFYWFEDCBZ"
Returns: "BCDEF"
We see that the reverse of BCDEF is FEDCB, which appears later in the string.  
1)   
      "XYZ"
Returns: "X"
The best we can do is find a one character substring, so we implement the tie-breaker rule of taking the earliest one first.  
2)   
      "ABCABA"
Returns: "ABA"
The string ABA is a palindrome (it's its own reversal), so it meets the criteria.  
3)   
      "FDASJKUREKJFDFASIREYUFDHSAJYIREWQ"
Returns: "FDF"
 
4)   
      "ABCDCBA"
Returns: "ABCDCBA"
Here, the entire string is its own reversal.  

This problem statement is the exclusive and proprietary property of TopCoder, Inc. Any unauthorized use or reproduction of this information without the prior written consent of TopCoder, Inc. is strictly prohibited. (c)2003, TopCoder, Inc. All rights reserved.
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Here is my C++ solution

Solution:

#include <iostream>
#include <string>

using namespace std;

class ReverseSubstring
{
public:
 ReverseSubstring(string input)
 {
  str = input;
 }

 string findReversed(string input);

 string str;
};

string ReverseSubstring::findReversed(string input)
{
 char buf[51];
 for(int i = 0; i < input.size() && i < 50; ++i)
 {
  buf[i] =  input[i];
 }

 char tmp;
 for(int j = i; j > i / 2; j--)
 {
  tmp = buf[j - 1];
  buf[j - 1] = buf[i - j];
  buf[i - j] = tmp;
 }
 buf[i] = '/0';

 for(int l = input.size(); l >= 2; --l) //length
 {
  for(int s = 0; s <= input.size() - l; ++s)  //start point
  {
   string target(buf);
   int re = target.find(input.substr(s,l));
   if(re <= 50 && re >= 0)
   {
    return input.substr(s,l);
   }
  }
 }

 return input.substr(0,1);
}

int main()
{
 ReverseSubstring str("ABCDCBA");
 cout << str.findReversed(str.str);
 return 0;
}