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
#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\n", solve());
	}
    return 0;
}