确定当前已知能匹配到的最长处,看是否要更新最长
#include <bits/stdc++.h>
using namespace std;
const int N = 210005;
int p[N];
char str[N], s[N];
int main() {
while (~scanf("%s", str)) {
int n = strlen(str);
for (int i = 0; i<n; i++) {
s[2 * i] = '#';
s[2 * i + 1] = str[i];
}
s[2 * n] = '#';
s[2 * n + 1] = ' ';
n = 2 * n + 1;
int j = 0, mx = 0, id = 0;
for (int i = 0; i < n; i++)p[i] = 0;
for (int i = 0; i<n; i++) {
if (i > mx)mx = i, id = i;
j = id + id - i;
if (j>=0&&j<n&&j - p[j]<=id + id - mx) {
while (mx + 1 < n&&i + i - mx - 1 >= 0 && s[mx + 1] == s[i + i - mx - 1]) {
mx++;
p[i] = mx - i;
id = i;
}
}
else p[i] = p[j];
}
int ans = 0;
for (int i = 0; i<n; i++)
ans = max(ans, p[i]);
printf("%d
", ans);
}
return 0;
}