Manacher(最大回文字串)

很好的讲解

注意两端的字符要不同，同时数组要开大一些

【Manacher】最长回文子串

#include<bits/stdc++.h>
#define REP(i, a, b) for(register int i = (a); i < (b); i++)
#define _for(i, a, b) for(register int i = (a); i <= (b); i++)
using namespace std;

const int MAXN = 3e5 + 10;
int p[MAXN], len;
char a[MAXN], s[MAXN];

int init()
{
    a[0] = '|'; a[1] = '#';
    int j = 2;
    REP(i, 0, len)
    {
        a[j++] = s[i];
        a[j++] = '#';
    }
    a[j] = '&'; return j;
}

int solve()
{
    int n = init();
    int max_len = -1, last_r = 0, id = 0;
    REP(i, 1, n) 
    {
        if(i < last_r) p[i] = min(p[2 * id - i], last_r - i);
        else p[i] = 1;
        while(a[i + p[i]] == a[i - p[i]]) p[i]++;
        if(last_r < i + p[i])
        {
            last_r = i + p[i];
            id = i;
        }
        max_len = max(max_len, p[i] - 1);
    }
    return max_len;
}
 
int main()
{
    while(~scanf("%s", s))
    {
        len = strlen(s);
        printf("%d
", solve());
    }
    return 0;
}