USACO SEC.1.3 No.3 Calf Flac

题意：给出一篇文章，求略去其中的空格等各种字符（剩余大小写字母后）文中的最长回文子串，输出长度并打印原文中对应的字符串

核心：枚举回文串

        枚举回文串的中点下标是一个比较好的方法，如果反复枚举回文起始点复杂度太大

        枚举中点分为两种情况（长度为奇数和偶数），分别处理即可

        本题目输入的方式略麻烦

 

/*
ID: lsswxr1
PROG: calfflac
LANG: C++
*/
#include <iostream>
#include <vector>
#include <map>
#include <list>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cctype>
#include <cstdio>
#include <iomanip>
#include <cmath>
#include <cstdio>
#include <string>
#include <cstring>
#include <fstream>
using namespace std;

///宏定义
const int  INF = 1000000000;
const int MAXN = 20015;
const int maxn = MAXN;
///全局变量 和 函数

#define USACO
#ifdef USACO
#define cin fin
#define cout fout
#endif
//////////////////////////////////////////////////////////////////////////
char src[maxn], txt[maxn];
int reflect[maxn];
int cntTxt, cntSrc;
int ans1, ans2, anslen;
inline bool ok(char s1, char s2)
{
    int a1 = s1 - 'a';
    int a2 = s1 - 'A';
    int b1 = s2 - 'a';
    int b2 = s2 - 'A';
    if (a1 == b1 || a1 == b2 || a2 == b1 || a2 == b2)
        return true;
    return false;
}
int main()
{
#ifdef USACO    
    ofstream fout ("calfflac.out");
    ifstream fin ("calfflac.in");
#endif    
    ///变量定义
    string src_;
    cntSrc = 0;
    cntTxt = 0;
    while (getline(cin, src_))
    {
        int len = src_.length();
        for (int i = 0; i < len; i++)
        {
            src[cntSrc] = src_[i];
            if ((src[cntSrc] >= 'a' && src[cntSrc] <= 'z') || (src[cntSrc] >= 'A' && src[cntSrc] <= 'Z') )
            {
                txt[cntTxt] = src[cntSrc];
                reflect[cntTxt] = cntSrc;
                cntTxt++;
            }
            cntSrc++;
        }
        src[cntSrc++] = '\n';
    }
    src[cntSrc] = '\0';
    bool flag;
    anslen = 1;
    for (int midpos = 0; midpos < cntTxt; midpos++)
    {
        int maxlen = 0;
        //奇数
        int ll = midpos - 1;
        int rr = midpos + 1;
        maxlen = 1;
        while (ll >= 0 && rr < cntTxt)
        {
            if (ok(txt[ll], txt[rr]))
            {
                maxlen += 2;
                ll--;
                rr++;
            }
            else
                break;
        }
        if (maxlen > anslen)
        {
            anslen = maxlen;
            ans1 = reflect[ll + 1];
            ans2 = reflect[rr - 1];
        }
        //偶数
        ll = midpos - 1;
        rr = midpos;
        maxlen = 0;
        while (ll >= 0 && rr < cntTxt)
        {
            if (ok(txt[ll], txt[rr]))
            {
                maxlen += 2;
                ll--;
                rr++;
            }
            else
                break;
        }
        if (maxlen > anslen)
        {
            anslen = maxlen;
            ans1 = reflect[ll + 1];
            ans2 = reflect[rr - 1];
        }
    }
    cout << anslen << endl;
    for (int i = ans1; i <= ans2; i++)
    {
        cout << src[i];
    }
    cout << endl;

    ///结束
    return 0;
}