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  1 #include <cstdio>
  2 #include <cstring>
  3 #include <algorithm>
  4 using namespace std;
  5 const int maxn = 5e5 + 10;
  6 const int maxsize = 27;
  7 
  8 int par[maxn];
  9 int rnk[maxn];
 10 char s1[20], s2[20];
 11 int vis[maxn];
 12 int ch[maxn][maxsize];
 13 int val[maxn];
 
 14 
 15 int t;
 16 
 17 void init() {
 18     for (int i = 0; i < maxn; i++) {
 19         par[i] = i;
 20         rnk[i] = 0;
 21     }
 22 }
 23 
 24 int find(int x) {
 25     if (par[x] == x) return x;
 26     else return par[x] = find(par[x]);
 27 }
 28 
 29 void unite(int x, int y) {
 30     x = find(x);
 
 31     y = find(y);
 32     if (x == y) return;
 33 
 34     if (rnk[x] < rnk[y]) {
 35         par[x] = y;
 36     } else {
 37         par[y] = x;
 38         if (rnk[x] == rnk[y]) rnk[x]++;
 39     }
 40 }
 41 
 42 bool same(int x, int y) {
 43     return find(x) == find(y);
 44 }
 45 
 46 struct
 
 Tire {
 47     int sz;
 48     Tire() {
 49         sz = 1;
 50         memset(ch[0], 0, sizeof(ch[0]));
 51     }
 52     int idx(char c) {return c - ‘a‘;}
 53 
 54     int FFF(char* s) {
 55         int len = strlen(s);
 56         int u = 0;
 57         for (int i = 0; i < len; i++) {
 58             int c = idx(s[i]);
 59             if (!ch[u][c]) {
 60                 memset(ch[sz], 0, sizeof(ch[sz]));
 61                 val[sz] = 0;
 62                 ch[u][c] = sz++;
 63             }
 64             u = ch[u][c];
 65         }
 66         if (!val[u]) val[u] = t++;
 67         return val[u];
 68     }
 69 
 70 };
 71 
 72 
 73 
 74 int main() {
 75     init();
 76     int tag = 0;
 77     Tire Tree;
 78     t = 1;
 79     while (~scanf("%s%s", s1, s2)) {
 80         int a = Tree.FFF(s1), b = Tree.FFF(s2);
 81         vis[a]++; vis[b]++;
 82         if (!same(a, b)) {
 83             unite(a, b);
 84         }
 85         tag++;
 86         //if (tag == 5) break;
 87     }
 88     int odd = 0;
 89     bool flag = 1;
 90     for (int i = 1; i < t && flag; i++) {
 91         if (vis[i] & 1) odd++;
 92         if (find(i) != find(1)) flag = 0;
 93     }
 94     if (odd != 0 && odd != 2) {
 95         flag = 0;
 96     }
 97     if (flag) {
 98         puts("Possible");
 99     } else {
100         puts("Impossible");
101     }
102     return 0;
103 }

POJ2513Colored Sticks(歐拉路加字典樹）