ural 1297 最长回文串 manacher 算法

算法内容 http://blog.sina.com.cn/s/blog_70811e1a01014esn.html

题目直接看输出即可， 注意前后放 ? #, #*. 然后找最大回文串长度应该是 rid[i]*2 + (str[i] =='#')

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<string>
using namespace std;

const int N = 1024;

char s[N];
int rid[N<<2];
string t;
void init(){
    int len = strlen(s);
    t += '?';
    for(int i = 0; i < len; i++){
        t += '#';
        t += s[i];
    }
    t += "#*";
}
void GetRid(){
    int i = 1;
    for(int i=1,j=0,k,End=(int)t.size(); i < End-1; ){
        while( t[i-j-1] == t[i+j+1] ) j++;
        rid[i] = j;
        for(k = 1; k<=j && rid[i-k]!=rid[i]-k; k++)
            rid[i+k] = min( rid[i-k], rid[i]-k );
        i += k;
        j = max( j-k, 0 );
    }
}
int main(){
    
    scanf("%s", s );
    init();    
    GetRid();
        
    int len = (int)t.size();
    int m = 0, pos = -1;
    for(int i = 1; i < len-1; i++){
        if( m < (rid[i]*2+(t[i]!='#')) ){
            m = (rid[i]*2+(t[i]!='#')), pos = i;    
        }    
    }
    string ans;
    for(int i = pos-rid[pos]; i < pos+rid[pos]; i++){
        if( t[i] != '#' ) ans += t[i];    
    }
    printf("%s\n", ans.c_str() );
//    for(int i = 0; i < len; i++){
//        printf("%c ", t[i]);    
//    }puts("");
//    for(int i = 0; i < len; i++)
//        printf("%d ", rid[i] );    
//    puts("");    
    return 0; }