1 #include <cstdio>  2 #include <cstring>  3 #include <cstdlib>  4   5 #define MAXN  500005  6 #define MAXL  11  7 #define TRIEN 26  8   9 typedef struct Trie { 10     int v; 11     Trie *next[TRIEN]; 12     Trie() { 13         v = 0; 14         for (int i=0; i<TRIEN; ++i) 15             next[i] = NULL; 16     } 17 } Trie; 18  19 Trie root; 20 int pre[MAXN], deg[MAXN], n = 1; 21  22 void create(char str[], int in) { 23     int i = 0, id; 24     Trie *p = &root, *q; 25  26     while (str[i]) { 27         id = str[i] - ‘a‘; 28         ++i; 29         if (p->next[id] == NULL) { 30             q = new Trie(); 31             p->next[id] = q; 32         } 33         p = p->next[id]; 34     } 35     p->v = in; 36 } 37  38 int Tfind(char str[]) { 39     int i = 0, id; 40     Trie *p = &root; 41  42     while (str[i]) { 43         id = str[i] - ‘a‘; 44         ++i; 45         if (p->next[id] == NULL) 46             return 0; 47         p = p->next[id]; 48     } 49  50     return p->v; 51 } 52  53 int find(int x) { 54     return x==pre[x] ? x:pre[x]=find(pre[x]); 55 } 56  57 void merge(int a, int b) { 58     a = find(a); 59     b = find(b); 60     if (a != b) 61         pre[b] = a; 62 } 63  64 bool judge() { 65     int cnt = 0, i; 66     if (n == 1) 67         return true; 68     for (i=1; i<n; ++i) { 69         if (pre[i] == i) 70             ++cnt; 71         if (cnt > 1) 72             return false; 73     } 74     if (!cnt) 75         return false; 76     cnt = 0; 77     for (i=1; i<n; ++i) 78         if (deg[i] & 1) 79             ++cnt; 80     if (cnt==0 || cnt==2) 81         return true; 82     else 83         return false; 84 } 85  86 int main() { 87     char a[MAXL], b[MAXL]; 88     int i, k; 89  90     memset(deg, 0, sizeof(deg)); 91     for (i=0; i<MAXN; ++i) 92         pre[i] = i; 93  94     while (scanf("%s %s", a, b) != EOF) { 95         k = Tfind(a); 96         if (k) 97             deg[k]++; 98         else { 99             create(a, n);100             k = n;101             deg[n++] = 1;102         }103         i = Tfind(b);104         if (i)105             deg[i]++;106         else {107             create(b, n);108             i = n;109             deg[n++] = 1;110         }111         merge(k, i);112     }113 114     if (judge())115         printf("Possible\n");116     else117         printf("Impossible\n");118 119     return 0;120 }