Colored Sticks

Time Limit: 5000MS	Memory Limit: 128000K
Total Submissions: 23160	Accepted: 6107

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. 挺綜合的一題，有TRIE，有並查集，還要用歐拉回路的知識

#include<stdio.h>
#include<string.h>

#define maxn 600000
#define kind 26
#define clear(a,b) memset(a,b,sizeof(a))

int fa[maxn],l = 0;
int deg[maxn];
struct node{
  int num;
  struct node *next[kind];
  node(){
    num = 0;
    clear(next,NULL);
    }
  } *root;

int build(struct node *T, char s[])
{
    int i = 0,k;
    struct node *t = T;
    while(s[i]) {
       k = s[i] - 'a';
       if (t->next[k] == NULL) t->next[k] = new node();
       t = t->next[k];
       i++;
       }
    t->num = ++l;
    return l;
}

int find(struct node *T,char s[])
{
    int i = 0,k;
    struct node *t = T;
    while(s[i]) {
        k = s[i] - 'a';
        if (t->next[k] == NULL) return 0;
        t = t->next[k];
        i++;
        }
    return t->num;
}

int getfa(int t)
{
   while(t != fa[t]) t = fa[t];
   return t;
}

int judge(int a,int b)
{
  return getfa(a) == getfa(b);
}

void unfa(int a,int b)
{
   fa[b] = getfa(a);
}

int work()
{
  int i,t1,t2,tmp;
  char s1[20],s2[20];
  root = new node();
  clear(deg,0);
  for(i = 1;i < maxn;i++) fa[i] = i;
  while (scanf("%s%s",s1,s2) != EOF) {
  //    if (s1[0] == '0') break;
      if ((t1 = find(root,s1)) == 0) t1 = build(root,s1);
      if ((t2 = find(root,s2)) == 0) t2 = build(root,s2);
      if (!judge(t1,t2)) unfa(t1,t2);
  //    printf("%d %d\n",t1,t2);
      deg[t1]++;
      deg[t2]++;
      }
  if (l == 0) return 1;
  tmp = getfa(1);
  t1 = 0;
  t2 = 0;
  for(i = 2;i <= l;i++) if (getfa(i) != tmp) return 0;
  for(i = 1;i <= l;i++) if (deg[i] & 1) t1++;
                                else t2++;
  if (t1 == 0) return 1;
  if (t1 == 2) return 1;
  return 0;
}

int main()
{
  if (work()) printf("Possible\n");
    else printf("Impossible\n");
  return 0;
}