字符串 Alex_Wei

#include <bits/stdc++.h>
using namespace std;
const int N = 2.2e7 + 5;
int n, m, ans, R[N];
char s[N], t[N];
int main() {
  scanf("%s", s + 1), n = strlen(s + 1);
  t[0] = '!', t[m = 1] = '@';
  for(int i = 1; i <= n; i++) t[++m] = s[i], t[++m] = '@';
  t[++m] = '#';
  for(int i = 1, c = 0, r = 0; i < m; i++) {
    R[i] = r < i ? 0 : min(R[c * 2 - i], r - i + 1);
    while(t[i - R[i]] == t[i + R[i]]) R[i]++;
    ans = max(ans, R[i] - 1);
    if(i + R[i] - 1 > r) c = i, r = i + R[i] - 1;
  }
  cout << ans << endl;
  return 0;
}

scanf("%s" , c1 + 1);
scanf("%s" , c2 + 1);
int len1 = strlen(c1 + 1) , len2 = strlen(c2 + 1);
z[1] = len2;
for(int i = 2 , l = 0 , r = 0;i <= len2;i ++) {
	z[i] = i > r ? 0 : min(z[i - l + 1] , r - i + 1);
	while(c2[1 + z[i]] == c2[i + z[i]]) z[i] ++;
	if(i + z[i] - 1 > r) {
		l = i , r = i + z[i]- 1;
	}
}

for(int i = 1 , l = 0 , r = 0;i <= len1;i ++) {
	p[i] = i > r ? 0 : min(z[i - l + 1] , r - i + 1);
	while(p[i] < len2 && c2[1 + p[i]] == c1[i + p[i]]) p[i] ++;
	if(i + p[i] - 1 > r) {
		l = i , r = i + p[i] - 1;
	} 
}