#include<iostream>
using namespace std;// brute force
string findLongestPalindrome_1(string &str){int length=str.size();int maxLength=0;int start;for(int i=0;i<length;i++){for(int j=i+1;j<length;j++){int left,right;for(left=i,right=j;left<right;left++,right--){if(str[left]!=str[right])break;}if(left>=right && (j-i)>maxLength){maxLength=j-i+1;start=i;}}}if(maxLength>0)return str.substr(start,maxLength);return NULL;
}// dynamic programming
string findLongestPalindrome_2(string &str){const int length=str.size();int maxLength=1;int start;bool dp[length][length];for(int i=0;i<length;i++)for(int j=0;j<length;j++)dp[i][j]=false;for(int i=0;i<length;i++){dp[i][i]=true;if(i<length-1 && str[i]==str[i+1]){dp[i][i+1]=true;start=i;maxLength=2;}}for(int len=3;len<=length;len++){for(int i=0;i<=length-len;i++){int j=i+len-1;if(dp[i+1][j-1] && str[i]==str[j]){dp[i][j]=true;start=i;maxLength=len;}}}if(maxLength>=2)return str.substr(start,maxLength);return NULL;
}// pivot expand
string findLongestPalindrome_3(string &str){const int length=str.size();int maxLength=1;int start;for(int i=0;i<length;i++){int left=i-1;int right=i+1;while(left>=0 && right<=length-1 && str[left]==str[right]){if(right-left+1>maxLength){start=left;maxLength=right-left+1;}left--;right++;}}for(int i=0;i<length;i++){int left=i;int right=i+1;while(left>=0 && right<=length-1 && str[left]==str[right]){if(right-left+1>maxLength){start=left;maxLength=right-left+1;}left--;right++;}}if(maxLength>0)return str.substr(start,maxLength);return NULL;
}int main(){string str="ababcddcbbd";cout<<findLongestPalindrome_1(str)<<endl;cout<<findLongestPalindrome_2(str)<<endl;cout<<findLongestPalindrome_3(str)<<endl;return 0;
}