Longest Palindromic Substring

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

class Solution {
public:
     string longestPalindrome( string s) 
    {
         int n=s.length();
         int longest[n];
         int max= 1;
         int pend= 0;
         // 1 3 5 
         for( int i= 0;i<n;i++) longest[i]= 1;
        
         for( int l= 3;l<=n;l=l+ 2)
        {
             for( int i=n- 1;i>=- 1;i--)
                 if(longest[i- 1]==l- 2 && s[i]==s[i-l+ 1])
                {
                    longest[i]=l;
                     if(max<l)
                    {
                        max=l;pend=i;
                    }
                }
        }
         // 2 4 6
         for( int i= 0;i<n;i++) longest[i]= 0;
         for( int l= 2;l<=n;l=l+ 2)
        {
             for( int i=n- 1;i>=- 1;i--)
                 if(longest[i- 1]==l- 2 && s[i]==s[i-l+ 1])
                {
                    longest[i]=l;
                     if(max<l)
                    {
                        max=l;pend=i;
                    }
                }
        }
         string result= "";
         for( int i=pend;i>=pend-max+ 1;i--)
            result=s[i]+result;
         return result;
    }
};