• 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 expandAroundCenter(string s, int c1, int c2) {
int l = c1, r = c2;
int n = s.length();
while (l >= 0 && r <= n-1 && s[l] == s[r]) {
l–;
r++;
}
return s.substr(l+1, r-l-1);
}

string longestPalindrome(string s) {
int n =s.length();
if (n == 0) return “”;
string longest=s.substr(0,1);
for(int i=0 ; i<n ;i++)
{
string p1 = expandAroundCenter(s, i, i);
if (p1.length() > longest.length())
longest = p1;

string p2 = expandAroundCenter(s, i, i+1);
if (p2.length() > longest.length())
longest = p2;
}
return longest;
}
};

Runtime : 280 ms