view code//第一次用指针写trie,本来是用二维数组，发现数组开不下，只好删删改改，改成指针//做这道题，知道了欧拉回路判定，还有用指针写trie#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <queue>using namespace std;const int N = 500010;char s1[15], s2[15];int fa[N], u, v, in[N], color =1;struct Trie{    Trie *ch[26];    int val;    void init()    {        for(int i=0; i<26; i++) ch[i] = NULL;        val = 0;    }    Trie()    {        for(int i=0; i<26; i++) ch[i] = NULL;        val = 0;    }    int idx(char c){return c-‘a‘; }    int ins_find(char *s, Trie *t)    {        int  n = strlen(s);        for(int i=0; i<n; i++)        {            int c = idx(s[i]);            if(!t->ch[c])            {                t->ch[c] = new Trie();            }            t = t->ch[c];        }        if(!t->val) t->val = color++;        return t->val;    }}*tr;int find(int x){    if(fa[x]<0) return x;    return fa[x]=find(fa[x]);}int main(){//    freopen("in.txt", "r", stdin);    memset(fa, -1, sizeof(fa));    tr = new Trie();    while(scanf("%s%s", s1, s2)>0)    {        u = tr->ins_find(s1, tr), v = tr->ins_find(s2, tr);        in[u]++, in[v]++;        u = find(u), v = find(v);        if(u!=v) fa[u] = v;    }    int num1=0, num2=0;    for(int i=1; i<color; i++)    {        if(in[i]&1) num1++;        if(fa[i]==-1) num2++;    }    if((num1==0 || num1==2) && num2<2)        puts("Possible");    else puts("Impossible");    return 0;}