LeetCode:Longest Palindromic Substring 最长回文子串

//核心代码
class Solution {
public:
string longestPalindrome(string s) {
const int len = s.size();
if(len <= 1)return s;
//Manncher算法 ，o（n）
string str = preProcess(s);
int n = str.size(), id = 0, mx = 0;
vector<int>p(n, 0);
for(int i = 1; i < n-1; i++)
{
p[i] = mx > i ? min(p[2*id-i], mx-i) : 1;
//if(mx <= i || (mx > i && p[2*id-i] == mx - i)) //根据正文斜体部分的注释，这里可要可不要
while(str[i+p[i]] == str[i-p[i]])p[i]++;
if(i + p[i] > mx)
{
mx = i + p[i];
id = i;
}
}

//遍历p，寻找最大回文长度
int maxLen = 0, index = 0;
for(int i = 1; i < n-1; i++)
if(p[i] > maxLen)
{
maxLen = p[i];
index = i;
}
return s.substr((index - maxLen)/2, maxLen-1);
}
//预处理字符串，abc预处理后变成$#a#b#c#^
string preProcess(const string &s)
{
int n = s.size();
string res;
res.push_back('$');//把$放到字符串头部
res.push_back('#');//以#作为原来字符串中每个字符的间隔
for(int i = 0; i < n; i++)
{
res.push_back(s[i]);
res.push_back('#');
}
res.push_back('^');//以^作为字符串的结尾
return res;
}
};