Solution.cpp

class Solution {
public:
 int maxLen;
 int start;
 string longestPalindrome(string s) {
 if (s.size()<2) return s;
 for(int i=0;i<s.size()-1;i++) {
 extendPalindrom(s, i, i); //assume odd lenght, try to extend as long as possible
 extendPalindrom(s, i, i+1); //assume even lenght
 }
 return s.substr(start, maxLen);
 }

 void extendPalindrom(string str, int s, int e) {
 while(s>=0 && e<str.size() && str[s]==str[e]) {
 s--;
 e++;
 }
 if(maxLen<e-s-1) { //we have e+1 after prev increment
 start=s+1; //we have s-1 after prev decrement
 maxLen=e-s-1;
 }
 }

};