原题链接：http://ac.jobdu.com/problem.php?pid=1528
小白书上的做法，不过这个还要简单些。。。
1 #include<algorithm> 2 #include<iostream> 3 #include<cstdlib> 4 #include<cstring> 5 #include<cstdio> 6 using std::max; 7 const int Max_N = 200010; 8 char ret[Max_N]; 9 void solve() { 10 int i, j, ans = 0, n = strlen(ret); 11 for (i = 0; i < n; i++) { 12 for (j = 0; i >= j && i + j < n; j++) { 13 if (ret[i - j] != ret[i + j]) break; 14 ans = max(ans, j << 1 | 1); 15 } 16 for (j = 0; i >= j && i + j + 1 < n; j++) { 17 if (ret[i - j] != ret[i + j + 1]) break; 18 ans = max(ans, (j << 1) + 2); 19 } 20 } 21 printf("%d ", ans); 22 } 23 int main() { 24 #ifdef LOCAL 25 freopen("in.txt", "r", stdin); 26 freopen("out.txt", "w+", stdout); 27 #endif 28 while (gets(ret)) solve(); 29 return 0; 30 }