[let code]5.最长回文子串

the question：

analysis：

1. you should find the last longest Palindrome like the frist instance “aba”;
2. spilt the string ,and judge the substr;
3. find the pos and longest length;
4. return the right substr;
5. this program just found the result , you should try to reduce the time and space complex.

code：

bool is(string s, int i, int j)
{
  int t = i+j-1;
  for (i; i <= t ; i++)
  {
      if (s[i] != s[t--])
          return false;
  }
  return true;
}
string longestPalindrome(string s)
{
  int pos = 0, max = 0, n = s.size();
  for (int i = 0; i < n; i++)
  {
	   for (int j = n - i; j >= 1; j--)
	   {
	          if (j >= max && is(s, i, j))
	          {
	           max = j;
	           pos = i;
	          }	   
	  }
  }
  return s.substr(pos, max);
}

result：