Extend to Palindrome UVA - 11475（补成回文串）

题意：

　　就是用最少的字符把原字符串补成回文串

解析：

　　emm/。。。/网上都是用kmp和后缀数组做的 我没想到这俩的思路。。。emmm。。。

想到了exkmp的  就是原串和逆串匹配一下  注意要保证这个匹配的最大长度 要到原串的结尾

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cstring>
#include <map>
#include <cctype>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#define rap(i, a, n) for(int i=a; i<=n; i++)
#define rep(i, a, n) for(int i=a; i<n; i++)
#define lap(i, a, n) for(int i=n; i>=a; i--)
#define lep(i, a, n) for(int i=n; i>a; i--)
#define rd(a) scanf("%d", &a)
#define rlld(a) scanf("%lld", &a)
#define rc(a) scanf("%c", &a)
#define rs(a) scanf("%s", a)
#define MOD 2018
#define LL long long
#define ULL unsigned long long
#define Pair pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define _  ios_base::sync_with_stdio(0),cin.tie(0)
//freopen("1.txt", "r", stdin);
using namespace std;
const int maxn = , INF = 0x7fffffff;
int nex[maxn], ex[maxn];
char s1[maxn], s2[maxn];
void get_next(char *s)
{
    int i=, j, po, len = strlen(s);
    nex[] = len;
    while(s[i] == s[i+] && i+ < len)
        i++;
    nex[] = i;
    po = ;
    for(int i=; i<len; i++)
    {
        if(i+nex[i-po] < po + nex[po])
            nex[i] = nex[i-po];
        else
        {
            j = po + nex[po] - i;
            if(j < ) j = ;
            while(i + j < len && s[i+j] == s[j])
                j++;
            nex[i] = j;
            po = i;
        }
    }
}

void get_ex(char *s1, char *s2)
{
    int i=, j, po, len1 = strlen(s1), len2 = strlen(s2);
    get_next(s2);
    while(s1[i] == s2[i] && i < len1 && i < len2)
        i++;
    ex[] = i;
    po = ;
    for(int i=; i<len1; i++)
    {
        if(i + nex[i - po] < po + ex[po])
            ex[i] = nex[i-po];
        else
        {
            j = po + ex[po] - i;
            if(j < ) j = ;
            while(i + j < len1 && j < len2 && s1[i+j] == s2[j])
                j++;
            ex[i] = j;
            po = i;
        }
    }
}

int main()
{
    while(~scanf("%s", s1))
    {
        int len = strlen(s1);
        strcpy(s2, s1);
        reverse(s2, s2+len);
        get_next(s2);
        get_ex(s1, s2);
        if(ex[] == len)
        {
            cout<< s1 <<endl;
            continue;
        }
        int maxx = -INF, id;
        for(int i=; i<len; i++)
            if(maxx < ex[i] && i + ex[i] == len)
            {
                maxx = ex[i];
                id = i;
            }
     //   cout<< maxx <<endl;
        if(maxx == )
        {
            cout<< s1;
            cout<< s2+ <<endl;
            continue;
        }
        cout<< s1;
        for(int i=id-; i>=; i--)
            cout<<s1[i];
        cout<<endl;

    }

    return ;
}