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  1. #include <iostream>
  2. #include <string>
  3. #include <algorithm>
  4. using namespace std;
  5.  
  6. bool isPalindrome(string s)
  7. {
  8.     if (s.length()<2)    // empty strings and singles chars are no palindromes !
  9.         return false;   
  10.     for (auto f=s.cbegin(), r=s.cend()-1; f!=r;  r--) {
  11.     	if (*f!=*r)     // if the nth letter from start doesn't match nth from ens
  12.     	    return false;    // not a palindrom
  13.     	if (++f==r)    // if middle of string is between two chars
  14.     		break;     
  15.     }
  16.     return true;   // we meet in the middle so it's a palindrome 
  17. }
  18.  
  19. int startWithPalindome(const string a)
  20. {
  21. 	if (a.length()>1)
  22. 	{
  23.         for (int N = a.rfind(a[0]); N!=string::npos && N>0; N= a.rfind(a[0],N-1) ) {
  24.             if ( isPalindrome(a.substr(0,N+1)) )
  25.                 return N+1;
  26.         }
  27. 	}
  28.  
  29.     return -1;
  30. }
  31.  
  32. int main() {
  33. 	string s1 = "ABBA";
  34. 	string s2 = "ABXBA";
  35. 	string s3 = "ABCA";
  36.  
  37. 	cout << "Testing isPalindrome():"<<endl; 
  38. 	cout <<"  "<< s1 << ": " << (isPalindrome(s1) ? "Ok":"fail") <<endl; 
  39. 	cout <<"  "<< s2 << ": " << (isPalindrome(s2) ? "Ok":"fail") <<endl; 
  40. 	cout <<"  "<< s3 << ": " << (isPalindrome(s3) ? "Fail":"Ok") <<endl;
  41. 	cout <<endl; 
  42.  
  43. 	string b1=s1+"BLABL"; 
  44. 	string b2=s2+"BLABLA"; 
  45. 	string b3=s3+"BLABL";
  46.  
  47. 	cout << "Testing sart :"<<endl; 
  48. 	cout <<"  "<< b1 << ": " << startWithPalindome(b1)<<endl;  
  49. 	cout <<"  "<< b2 << ": " << startWithPalindome(b2)<<endl;  
  50. 	cout <<"  "<< b3 << ": " << startWithPalindome(b3)<<endl;  
  51.  
  52. 	// your code goes here
  53. 	return 0;
  54. }
Success #stdin #stdout 0s 3460KB
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stdin
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Standard input is empty
stdout
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Testing isPalindrome():
  ABBA: Ok
  ABXBA: Ok
  ABCA: Ok

Testing sart :
  ABBABLABL: 4
  ABXBABLABLA: 5
  ABCABLABL: -1
https://ideone.com/fBkZ7n
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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