Description

You are given a bunch of wooden sticks. Each endpoint of each stick is colored with some color. Is it possible to align the sticks in a straight line such that the colors of the endpoints that touch are of the same color?

Input

Input is a sequence of lines, each line contains two words, separated by spaces, giving the colors of the endpoints of one stick. A word is a sequence of lowercase letters no longer than 10 characters. There is no more than 250000 sticks.

Output

If the sticks can be aligned in the desired way, output a single line saying Possible, otherwise output Impossible.

Sample Input

blue red

red violet

cyan blue

blue magenta

magenta cyan

Sample Output

Possible

 

并查集①

code：

#include
      
        #include
       
         #define maxn 500005 int de[maxn]; int f[maxn]; int v[maxn]; int find(int x) {
    int r=x; while(r!=f[r])         r=f[r]; int i=x; int j; while(i!=r)     {
            j=f[i];         f[i]=r;         i=j;     } return r; } void join(int x,int y) {
    int fx=find(x); int fy=find(y); if(fx!=fy)     {
    if(fx
        
         2)         {
                printf("Impossible\n"); return 0;         }     }     tot=0; for(i=1;i
         
          1)         {
                printf("Impossible\n"); return 0;         }     }     printf("Possible\n"); return 0; }
         
        
       
      

并查集②：

 

#include
      
        #include
       
         #define maxn 500005 int de[maxn]; int f[maxn]; int find(int x) {
    int r=x; while(r!=f[r])   r=f[r]; int i=x; int j; while(i!=r)  {
      j=f[i];   f[i]=r;   i=j;  } return r; } void join(int x,int y) {
    if(find(x)==0)   f[x]=x; if(find(y)==0)   f[y]=y;  f[find(x)]=find(y); } int Hash(char s[]) {
    int i,hash=1; int len=strlen(s); for(i=0;i
        
         2)   {
       printf("Impossible\n"); return 0;   }  }  i=1; for(i=1;i
        
       
      

 

字典树：

 

#include
      
        #include
       
         #define maxn 500005 int de[maxn]; int f[maxn]; int num; struct node {
    int id,i;  node *next[26];  node()  {
      id=-1; for(i=0;i<26;i++)    next[i]=NULL;  } }*root; int find(int x) {
    int r=x; while(r!=f[r])   r=f[r]; int i=x; int j; while(i!=r)  {
      j=f[i];   f[i]=r;   i=j;  } return r; } void join(int x,int y) {
    if(find(x)==0)   f[x]=x; if(find(y)==0)   f[y]=y;  f[find(x)]=find(y); } int insert(char s[]) {
    int i;  node *p=root; int len=strlen(s); for(i=0;i
        
         next[s[i]-'a']==NULL)    p->next[s[i]-'a']=new node;   p=p->next[s[i]-'a'];  } if(p->id==-1)   p->id=num++; return p->id; } int main() {
     num=0;  root=new node; char a[11],b[11]; int p,q,flag; int i,sum; for(i=0;i
         
          2||flag!=find(i))   {
       printf("Impossible\n"); return 0;   }  }  printf("Possible\n"); return 0; }