题意

给一个字符串, 求最长回文镜像子串长度

思路

Manacher + 镜像判断 
算法实现 : Manacher算法总结

AC代码 ( kuangbin板子 )

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#define mst(a) memset(a,0,sizeof(a))
using namespace std;

const int maxn = 1e3+10;
int len;
char mrk[] = "A      HI   M O    TUVWXY ";
char Ma[maxn*2];
int Mp[maxn*2];

void Manacher( char s[], int len ){
    int l = 0;
    Ma[l++] = ‘$‘;
    Ma[l++] = ‘#‘;
    for( int i = 0; i < len; i++ ){
        Ma[l++] = s[i];
        Ma[l++] = ‘#‘;
    }
    Ma[l] = 0;
    int mx = 0, id = 0;
    for( int i = 0; i < l; i++ ){
        Mp[i] = mx > i ? min(Mp[2*id-i], mx-i) : 1;
        while( Ma[i+Mp[i]] == Ma[i-Mp[i]] && mrk[Ma[i+Mp[i]]-‘A‘] != ‘ ‘ && mrk[Ma[i-Mp[i]]-‘A‘] != ‘ ‘ ) Mp[i]++;
        if( i+Mp[i] > mx ){
            mx = i + Mp[i];
            id = i;
        }
    }
}

char s[maxn];

int main()
{
    int T;
    scanf("%d",&T);
    while(T--){
        mst(s);
        mst(Ma);
        mst(Mp);
        scanf("%s",s);
        len = strlen(s);
        Manacher(s, len);
        int ans = 0;
        for( int i = 0; i < 2*len+2; i++ )
            if( mrk[Ma[i]-‘A‘] != ‘ ‘ )
                ans = max(ans, Mp[i]-1);
        printf("%d\n",ans);
    }
    return 0;
}