Manacher's Algorithm 求最长回文子串

摘自：https://blog.csdn.net/MallowFlower/article/details/87701363
讲解：https://www.cnblogs.com/z360/p/6375514.html

#include 
using namespace std;
string Manacher(string s)
{
    // Insert '#'
    string t = "$#";
    for (int i = 0; i < s.size(); ++i)
    {
        t += s[i];
        t += "#";
    }
    // Process t
    vector<int> p(t.size(), 0);
    int mx = 0, id = 0, resLen = 0, resCenter = 0;//mx为延伸到最右边的位置
    for (int i = 1; i < t.size(); ++i)
    {
        p[i] = mx > i ? min(p[2 * id - i], mx - i) : 1;
        while (t[i + p[i]] == t[i - p[i]])//继续延伸
            ++p[i];
        if (mx < i + p[i])//更新延伸到最右边的位置与中心
        {
            mx = i + p[i];
            id = i;
        }
        if (resLen < p[i])//更新答案
        {
            resLen = p[i];
            resCenter = i;
        }
    }
    return s.substr((resCenter - resLen) / 2, resLen - 1);//(resCenter - resLen) / 2是起始位置
    //往后延伸resLen-1个字符就是终点
}

int main()
{
    string s1 = "12212";
    cout << Manacher(s1) << endl;
    string s2 = "122122";
    cout << Manacher(s2) << endl;
    string s = "waabwswfd";
    cout << Manacher(s) << endl;
}