暴力程序之回文子串

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <sstream>
#include <map>
#include <bitset>
using namespace std ;
#define zero {0}
#define INF 2000000000
#define eps 1e-6
typedef long long LL;
int Max=0;
char a[1000];
int n;
char it[100];
int  f(string s)
{
    //cout<<s<<endl;
    int len=s.size();
    int i,j,k;
    int maxx=1;
    string ss="";
    string re;
    for(i=0;i<len;i++)
    {
        ss+=s[i];
        for(j=i+1;j<len;j++)
        {
            ss+=s[j];
        //    cout<<ss<<endl;
            re=ss;
            reverse(re.begin(),re.end());
            if(ss==re)
            {
                maxx=max(int(ss.size()),maxx);
            }
        }
        ss="";
    }
    return maxx;
}
void dfs(int i)
{
     if (i!=n)
     {
          a[i]='a';
          dfs(i+1);
          a[i]='b';
          dfs(i+1);
     }
     else
     {
         if(f(string(a))<Max)
         {
             Max=f(string(a));
             strcpy(it,a);
             //printf("%s-------%d\n",a,Max);
         }
     }
}
int main()
{
    #ifdef DeBUG
        freopen("C:\\Users\\Sky\\Desktop\\1.in","r",stdin);
    //freopen("C:\\Users\\Sky\\Desktop\\打表.txt","w",stdout);//PLEASE DELETE IT!!!!!!!!!!!!!!!!!!!!!!!!
    #endif
    int i,j,k;
    string s;
    for(i=1;i<=20;i++)
    {
        Max=INF;
        memset(a,0,sizeof(a));
        n=i;
        printf("*****************长度%d\n",i);
        dfs(0);
        printf("%s\n",it);
    }
    
    return 0;
}

由a，b组成的包含最短的（最长回文子串）的序列，写这个暴力是解决一道题的关键hdu4731