周赛-Colored Sticks

Colored Sticks

Time Limit: 5000MS Memory Limit: 128000K

Total Submissions: 32423 Accepted: 8556

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

字典树+并查集+欧拉路径

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <list>
#include <algorithm>
#define LL long long
#define RR freopen("output.txt","r",stdoin)
#define WW freopen("input.txt","w",stdout)

using namespace std;

const int MAX = 2500000;

struct node
{
int num;
node *next[26];
}head;

int pre[MAX];

int Du[MAX];

int top;

char s[15],c[15];

node *Creat()
{
node *p;
p=new node;
p->num=0;
for(int i=0;i<26;i++)
{
p->next[i] =  NULL;
}
return p;
}

int Build_Tree(char *str)//建立字典树
{
int len=strlen(str);
int a;
node *p=&head;
for(int i=0;i<len;i++)
{
a=str[i]-'a';
if(p->next[a])
{
p=p->next[a];
}
else
{
p->next[a]=Creat();
p=p->next[a];
}
}
if(!p->num)//返回单词所在的位置
{
p->num=++top;
}
return p->num;
}
int Find(int x)//并查集+压缩路径
{
int i=x,j=x,s;
while(pre[i]!=-1)
{
i=pre[i];
}
while(pre[j]!=-1)
{
s=pre[j];
pre[j]=i;
j=s;
}
return i;
}
void Link(int x,int y)
{
int FX=Find(x);
int FY=Find(y);
if(FX!=FY)
{
pre[FX]=FY;
}
}
int main()
{
memset(pre,-1,sizeof(pre));
memset(Du,0,sizeof(Du));
top=0;
for(int i=0;i<26;i++)
{
head.next[i]=NULL;
}
// int n;
// scanf("%d",&n);
//for(int i=0;i<n;i++)
while(~scanf("%s %s",s,c))
{
// scanf("%s %s",s,c);
int u=Build_Tree(s);
int v=Build_Tree(c);
Du[u]++;
Du[v]++;
Link(u,v);
}
int ans=0,ant=0;
for(int i=1;i<=top;i++)
{
if(Du[i]%2)
{
ans++;
}
if(pre[i]==-1)
{
ant++;
}
if(ant>1||ans>2)//如果入度为奇数的超过2个，或者根大于一个就不能连成一条直线
{
break;
}
}
if(ant>1||ans>2)
{
printf("Impossible\n");
}
else
{
printf("Possible\n");
}
return 0;
}