[POJ3974]Palindrome

 1 #include <cstdio>
 2 #include <cstdlib>
 3 #include <cstring>
 4 #include <algorithm>
 5 #include <iostream>
 6 #include <cmath>
 7 #include <queue>
 8 #include <map>
 9 #include <stack>
10 #include <list>
11 #include <vector>
12 
13 using namespace std;
14 
15 const int maxn = 2222222;
16 int pre[maxn];
17 char str[maxn];
18 char tmp[maxn];
19 
20 inline int min(int x, int y) {
21     return x < y ? x : y;
22 }
23 
24 int init(char *tmp, char *str) {
25     int len = strlen(str);
26     tmp[0] = ‘$‘;
27     for(int i = 0; i <= len; i++) {
28         tmp[2*i+1] = ‘#‘;
29         tmp[2*i+2] = str[i];
30     }
31     len = 2 * len + 2;
32     tmp[len] = 0;
33     return len;
34 }
35 
36 void manacher(int *pre, char *tmp, int len) {
37     int id = 0;
38     int mx = 0;
39     for(int i = 1; i < len; i++) {
40         pre[i] = mx > i ? min(pre[2*id-i], mx-i) : 1;
41         while(tmp[i+pre[i]] == tmp[i-pre[i]]) {
42             pre[i]++;
43         }
44         if(pre[i] + i > mx) {
45             id = i;
46             mx = pre[i] + id;
47         }
48     }
49 }
50 
51 int main() {
52     int kase = 1;
53     // freopen("in", "r", stdin);
54     while(~scanf("%s", str) && strcmp(str, "END") != 0) {
55         memset(pre, 0, sizeof(pre));
56         memset(tmp, 0, sizeof(tmp));
57         int len = init(tmp, str);
58         manacher(pre, tmp, len);
59         int ans = 1;
60         for(int i = 0; i < len; i++) {
61             ans = max(ans, pre[i]);
62         }
63         printf("Case %d: %d\n", kase++, ans - 1);
64     }
65 }