Manacher("马拉车"算法)学习笔记
学习
参考自:马拉车算法(Manacher’s Algorithm)
笔记
代码
#include <iostream>
#include <algorithm>
#include <string>
#define _for(i, a) for(int i = 0; i < (a); ++i)
#define _rep(i, a, b) for(int i = (a); i <= (b); ++i)
using namespace std;
string manacher(const string &s) {
if (s.size() < 2) return s;
string t = "$#";
for (int i = 0, n = s.size(); i < n; ++i) {
t += s[i];
t += (i == n - 1 ? "#@" : "#");
}
int id = 0, mx = 0, index = 0, maxlength = -1, n = t.size();
int *p = new int[n];
_for(i, n) {
p[i] = mx > i ? min(p[2 * id - i], p[mx - i]) : 1;
while (i + p[i] < n && i - p[i] >= 0 && t[i + p[i]] == t[i - p[i]]) p[i]++;
if (mx < p[i] + i) {
mx = p[i] + i;
id = i;
}
if (maxlength < p[i] - 1) {
maxlength = p[i] - 1;
index = i;
}
}
index = (index - maxlength) / 2;
return s.substr(index, maxlength);
}
int main() {
string a = "abacdcabad";
cout << manacher(a);
return 0;
}