great article.

i however has some doubts why this is a O(n), let’s take the example aaaaaaaaa, in this case, it is obvious that each a will have to be expended, according to the above algorithm, therefore it would be O(n^2).

where did mess up?

thanks,

public static string GetLongestPelindrome()
{

string str = “dcfcdhihijkjihjfccccccccccabcdefggfedcba”;
int[] index = new int[str.Length];
int[] length = new int[str.Length];
char c;
int currentindex = 0, i = 0, j = 0, bMaxindex = 0, bMaxLength = 0, sMaxindex = 0, sMaxLength = 0;

if (str[0] == str[1])
{
currentindex = 0;
bMaxLength = 2;
}
else
{
currentindex = 1;
bMaxLength = 1;
}

for (i = 0; i < str.Length; i = j)
{
c = str[i];
for (j = i + 1; j < str.Length && str[j] == c; j++) ;
if (sMaxLength < j - i)
{
sMaxLength = j - i;
sMaxindex = i;
}
}

for (i = 2; i < str.Length; i++)
{
if (i == 16) i = i;
if (currentindex == (i - 1))
{
if (str[i] == str[i - 2])
{
bMaxLength = 3;
bMaxindex = i - 2;
currentindex = i - 2;
}
else if (str[i] == str[i-1])
{
bMaxLength = 2;
bMaxindex = i - 2;
currentindex = i - 1;
}
else
{
currentindex = i;
bMaxLength = 1;
bMaxindex = i;
}
}
else
{
if (currentindex - 1 sMaxLength)
{
sMaxLength = bMaxLength;
sMaxindex = bMaxindex;
}

}

return (str.Substring(sMaxindex, sMaxLength));

}

Actually I am not able to understand the lengths array formation correctly or the array represents the list of longest palindrome lengths by center.

Thanks in advance.

Take for example the following input, “aaaaaaaaaa”. The algorithm above will expand the center on every iteration.