[UVA1262]Password

 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 = 1000010;
16 int nb;
17 char b[maxn];
18 int pre[maxn];
19 int vis[maxn];
20 
21 //b是模式串，a是目标串
22 void getpre(char *b, int *pre) {
23     int j, k;
24     pre[0] = -1;
25     j = 0;
26     k = -1;
27     while(j < nb) {
28         if(k == -1 || b[j] == b[k]) {
29             j++;
30             k++;
31             pre[j] = k;
32         }
33         else {
34             k = pre[k];
35         }
36     }
37 }
38 
39 int main() {
40     // freopen("in", "r", stdin);
41     while(~scanf("%s", b)) {
42         memset(pre, 0, sizeof(pre));
43         memset(vis, 0, sizeof(vis));
44         nb = strlen(b);
45         if(nb < 3) {
46             printf("Just a legend\n");
47             continue;
48         }
49         getpre(b, pre);
50         for(int i = 0; i < nb; i++) {
51             vis[pre[i]] = 1;
52         }
53         int flag = 0;
54         while(pre[nb]) {
55             if(vis[pre[nb]]) {
56                 printf("%.*s\n", pre[nb], b);
57                 flag = 1;
58                 break;
59             }
60             nb = pre[nb];
61         }
62         if(!flag) {
63             printf("Just a legend\n");
64         }
65     }
66     return 0;
67 }