51nod1089 最长回文子串 V2（Manacher算法）

马拉车

#include<iostream>
#include<cstring>
using namespace std;
const int MAXN = 100010;
char A[MAXN * 2];
int B[MAXN * 2];

void Manacher(char s[], int len)
{
    int l = 0;
    A[l++] = '$';   
    A[l++] = '#';
    for (int i = 0; i < len; i++)
    {
        A[l++] = s[i];
        A[l++] = '#';
    }
    A[l] = 0;      
    int mx = 0;
    int id = 0;
    for (int i = 0; i < l; i++)
    {
        B[i] = mx > i ? std::min(B[2 * id - i], mx - i) : 1;
        while (A[i + B[i]] == A[i - B[i]])
        {
            B[i]++;
        }
        if (i + B[i] > mx)
        {
            mx = i + B[i];
            id = i;
        }
    }
    return ;
}


char s[MAXN];

int main()
{
    while (cin >> s)
    {
        int len = (int)strlen(s);
        Manacher(s, len);
        int ans = 0;
        for (int i = 0; i < 2 * len + 2; i++) 
        {
            ans = max(ans, B[i] - 1);
        }
        cout << ans <<endl;
    }

    return 0;
}