USACO Section 1.3 Calf Flac

/*
PROG : calfflac
LANG : C++
*/

# include <cstdio>
# include <cctype>

# define N 20000 + 5

int n;
char s
;

int Min(int x, int y)
{
return x < y ? x : y;
}

int manacher(char *s, int len, int &st)
{
int n = len*2+1;
char t[2 * N];

/*  insert '#' in string s to form a 2*len+1 string t
在 s 中插入 len+1 个 '#' 使 s 中的奇偶回文字符串统一起来   */
for (int i = 0; i < len; ++i)
{
t[2*i] = '#';
t[2*i+1] = s[i];
}
t[n-1] = '#';

int ret = 0;
int p[2 * N];
int mx = 0, id;
for (int i = 1; i < n; ++i)
{
p[i] = mx>i ? Min(p[2*id-i], mx-i):1;
while (t[i-p[i]] == t[i+p[i]]) ++p[i];
if (i+p[i] > mx) mx = i+p[i], id = i;
/*  find the longest sub-palindrome,
set ret and st(start position of LSP in s) */
if (p[i]-1 > ret)
{
ret = p[i] - 1;
st = (i-p[i]+1)/2;
}
}
return ret;
}

void solve(void)
{
int st;
int r
;
char ss
;
int k = 0;
for (int i = 0; i < n; ++i)
{
if (isalpha(s[i]))
{
r[k] = i;
ss[k++] = tolower(s[i]);
}
}
int len = manacher(ss, k, st);
s[r[st+len-1]+1] = 0;
printf("%d\n%s\n", len, s+r[st]);
}

int main()
{
freopen("calfflac.in", "r", stdin);
freopen("calfflac.out", "w", stdout);

n = 0;
while ((s[n++]=getchar()) != EOF) ;

solve();

fclose(stdin);
fclose(stdout);

return 0;
}