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.
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"
The similar as above.
4) "ABCDCBA"
Returns: "ABCDCBA"
Here, the entire string is its own reversal.
class ReverseSubstring
{
static void Main(string[] args)
{
string[] strings = new string[] { "XBCDEFYWFEDCBZ", "XYZ",
"FDASJKUREKJFDFASIREYUFDHSAJYIREWQ", "ABCDCBA" };
for ( int i=0 ; i < strings.Length ; ++i )
{
System.Console.WriteLine(FindReversed(strings[i]));
}
}
private static string FindReversed(string input)
{
string substring = string.Empty;
for ( int i=0 ; i < input.Length ; ++i )
{
for ( int j=0 ; j < input.Length ; ++j )
{
if ( input[i] == input[input.Length-1-j] )
{
if ( i == input.Length-1-j )
{
if ( substring.Length == 0 )
{
substring = input[i].ToString();
}
break;
}
else
{
int k = 0;
for ( ; k < input.Length-i-j ; ++k )
{
if ( input[i+k] != input[input.Length-1-j-k] ) break;
}
if ( substring.Length < k )
{
substring = input.Substring(i, k);
}
}
}
}
}
return substring;
}
}