LeetCode 5 Longest Palindromic Substring 最长回文子序列 manacher算法 string.substr 难度:2

string longestPalindrome(string s)
{
    char ch[2001];int p[2001];
    ch[2*s.size()] = 0;
    for(int i = 0; i < 2 * s.size(); i++)
    {
        if((i & 1) == 1)ch[i] = s[(i>>1)];
        else ch[i] = ‘ ‘;
    }
    int mx = 1,id = 0;
    p[0] = 1;
    int ss = 0,se = 0;
    for(int i = 1; ch[i]; i++)
    {
        if(mx <= i)
        {
            p[i] = 1;
        }
        else
        {
            p[i] = min(p[id * 2 - i],mx - i);
        }
        while(ch[i + p[i]] == ch[i - p[i]] && i >= p[i])
        {
            p[i]++;
        }
        if(p[i] + i > mx)
        {
            id = i;
            mx = p[i] + i;
        }
        int ts = (i - p[i] + 1)/2;
        int te = (i + p[i] - 2)/2;//Attention,dont calculate ‘ ‘
        if(te - ts >se - ss){
            se = te;ss = ts;
        }
    }
    return s.substr(ss,se -ss + 1);//Attention,substr(start,len)
}