POJ 2513 Colored Sticks【欧拉通路】

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<stdio.h>
#include<string.h>
#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<fy)
            f[fy]=fx;
        else f[fx]=fy;
    }
}
int Hash(char s[])
{
    int i,hash=1;
    int len=strlen(s);
    for(i=0;i<len;i++)
        hash=(hash*29+s[i]-'a')%maxn;
    return hash;
}
int main()
{
    char a[11],b[11];
    int i,p,q,tot;
    memset(de,0,sizeof(de));
    memset(v,0,sizeof(v));
    for(i=0;i<maxn;i++)
        f[i]=i;
    while(scanf("%s%s",a,b)!=EOF)
    {
        p=Hash(a);
        q=Hash(b);
        de[p]++;
        de[q]++;
        v[p]=1;
        v[q]=1;
        join(p,q);
    }
    tot=0;
    for(i=1;i<maxn;i++)
    {
        if(de[i]&1)
            tot++;
        if(tot>2)
        {
            printf("Impossible\n");
            return 0;
        }
    }
    tot=0;
    for(i=1;i<maxn;i++)
    {
        if(v[i]&&find(i)==i)
            tot++;
        if(tot>1)
        {
            printf("Impossible\n");
            return 0;
        }
    }
    printf("Possible\n");
    return 0;
}
 

并查集②：

 

#include<stdio.h>
#include<string.h>
#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<len;i++)
  hash=(hash*29+s[i]-'a')%maxn;
 return hash;
}
int main()
{
 char a[11],b[11];
 int i,p,q,tot,flag,fx;
 memset(de,0,sizeof(de));
 memset(f,0,sizeof(f));
 while(scanf("%s%s",a,b)!=EOF)
 {
  p=Hash(a);
  q=Hash(b);
  de[p]++;
  de[q]++;
  join(p,q);
 }
 tot=0;
 for(i=1;i<maxn;i++)
 {
  if(de[i]%2)
   tot++;
  if(tot>2)
  {
   printf("Impossible\n");
   return 0;
  }
 }
 i=1;
 for(i=1;i<maxn;i++)
 {
  if(find(i))
   break;
 }
 flag=find(i);
 for(;i<maxn;i++)
 {
  fx=find(i);
  if(fx&&fx!=flag)
  {
   printf("Impossible\n");
   return 0;
  }
 }
 printf("Possible\n");
 return 0;
}

 

字典树：

 

#include<stdio.h>
#include<string.h>
#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<len;i++)
 {
  if(p->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<maxn;i++)
 {
  de[i]=0;
  f[i]=i;
 }
 while(scanf("%s%s",a,b)!=EOF)
 {
  p=insert(a);
  q=insert(b);
  de[p]++;
  de[q]++;
  join(p,q);
 }
 sum=0;
 flag=find(0);
 for(i=0;i<num;i++)
 {
  if(de[i]&1)
   sum++;
  if(sum>2||flag!=find(i))
  {
   printf("Impossible\n");
   return 0;
  }
 }
 printf("Possible\n");
 return 0;
}