终于，我AC了马拉车算法555

#include <bits/stdc++.h>
using namespace std;
const int N = 2e7 + 10;
char s[N], t[N];
int p[N];
int manacher(string s, int len) {
    int l = 0;
    t[l++] = '$', t[l++] = '#';
    for (int i = 0; i < len; i++) t[l++] = s[i], t[l++] = '#';
    t[l] = 0;
    int r = 0, c = 0;
    for (int i = 0; i < l; i++) {
        int &P = p[i];
        P = r > i ? min(p[2 * c - i], r - i) : 1;
        while (t[i + P] == t[i - P]) P++;
        if (i + P > r) r = i + P, c = i;
    }
    int ans = 0;
    for (int i = 0; i < l; i++) ans = max(ans, p[i]);
    return ans - 1;
}
int main() {
    cin >> s;
    cout <<manacher(s, strlen(s));
    return 0;
}

上面是ac代码
但是我想请教一下。。。

#include <bits/stdc++.h>
using namespace std;
const int N = 2e7 + 10;
string s, t;
int p[N];
int manacher(string s, int len) {
    int l = 0;
    t[l++] = '$', t[l++] = '#';
    for (int i = 0; i < len; i++) t[l++] = s[i], t[l++] = '#';
    t[l] = 0;
    int r = 0, c = 0;
    for (int i = 0; i < l; i++) {
        int &P = p[i];
        P = r > i ? min(p[2 * c - i], r - i) : 1;
        while (t[i + P] == t[i - P]) P++;
        if (i + P > r) r = i + P, c = i;
    }
    int ans = 0;
    for (int i = 0; i < l; i++) ans = max(ans, p[i]);
    return ans - 1;
}
int main() {
    cin >> s;
    cout <<manacher(s, s.size());
    return 0;
}

下面的代码仅仅是改了一下，把$char$数组改成了$string$，为什么就会指针错误了捏？