poj 2513

欧拉回路+并查集（判断图的联通）+Tire树（快速查找字符串，并且记录相应点的度数）

Tire树相关知识http://zh.wikipedia.org/wiki/Trie

#include <iostream>
using namespace std;
const int maxc = 26;
const int maxn = 500001;
struct TrieNode
{
	int key;
	TrieNode * child[maxc];
	TrieNode()
	{
		key=-1;
		memset(child,0,sizeof(child));
	}
};
int count[maxn];
TrieNode * root;
int tot=-1;
int insert(char * s)
{
	if(root==NULL) root=new TrieNode;
	int did;
	TrieNode * tem=root;
	for(;*s!='\0';s++)
	{
		did=*s-'a';
		if(tem->child[did]==NULL)
			tem->child[did]=new TrieNode;
		tem=tem->child[did];
	}
	if(tem->key==-1)
		tem->key=++tot;
	count[tem->key]++;
	return tem->key;
}
struct UFSTree
{
	int val;
	int parent;
	int rank;
}t[maxn];
void init()
{
	for(int i=0;i<maxn;i++)
	{
		t[i].val=i;
		t[i].parent=i;
		t[i].rank=0;
	}
}
int find(int k)
{
	if(t[k].val!=t[k].parent)
		t[k].parent=find(t[k].parent);
	return t[k].parent; 
}
void Union(int p1,int p2)
{
	if(t[p1].rank>t[p2].rank)
		t[p2].parent=p1;
	else
	{
		t[p1].parent=p2;
		if(t[p1].rank==t[p2].rank)
			t[p2].rank++;
	}
}
int main()
{
	char f[11],s[11];
	init();
	while(scanf("%s %s",f,s)!=EOF)
	{
		int k1=insert(f);
		int k2=insert(s);
		int p1=find(k1);
		int p2=find(k2);
		if(p1!=p2)
			Union(p1,p2);
	}
	if(root==NULL) 
	{
		cout<<"Possible"<<endl;
		return 0;
	}
	int pa1=find(0);
	int flag=1,i;
	for(i=1;i<=tot;i++)
	{
		if(find(i)!=pa1)
		{
			flag=0;
			break;
		}
	}

	if(!flag)
		cout<<"Impossible"<<endl;
	else
	{
		int dam=0;
		for(i=0;i<=tot;i++)
		{
			if(count[i]%2!=0) dam++;
		}
		if(dam!=2&&dam!=0)
			cout<<"Impossible"<<endl;
		else
			cout<<"Possible"<<endl;
	}
	return 0;
}