POJ 2513 Colored Sticks （欧拉回路 + 字典树 +并查集）

Colored Sticks

Time Limit: 5000MS		Memory Limit: 128000K
Total Submissions: 27097		Accepted: 7175

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

Hint

Huge input,scanf is recommended.

Source

The UofA Local 2000.10.14

 

详细解释：http://blog.csdn.net/lyy289065406/article/details/6647445

 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>

using namespace std;

struct Trie{
    int x;
    Trie *next[26];
}*root,memory[5100000];

int deg[5100000],father[510000],cnt,tot;

Trie *create(){
    Trie *p=&memory[cnt++];
    for(int i=0;i<26;i++)
        p->next[i]=NULL;
    return p;
}

void InsertTrie(char *str,int x){
    Trie *loc=root;
    for(int i=0;str[i]!='\0';i++){
        int id=str[i]-'a';
        if(loc->next[id]==NULL)
            loc->next[id]=create();
        loc=loc->next[id];
    }
    loc->x=x;
}

int SearchTrie(char *str){
    Trie *loc=root;
    for(int i=0;str[i]!='\0';i++){
        int id=str[i]-'a';
        if(loc->next[id]==NULL)
            return 0;
        loc=loc->next[id];
    }
    return loc->x;
}

void init(){
    for(int i=1;i<=501000;i++)
        father[i]=i;
    memset(deg,0,sizeof(deg));
    cnt=0;
    tot=0;
}

int findSet(int x){
    if(x!=father[x]){
        father[x]=findSet(father[x]);
    }
    return father[x];
}

int judge(){        //判断是否满足欧拉 
    int odd=0;
    for(int i=1;i<=tot;i++)
        if(deg[i]%2==1)
            odd++;
    if(odd!=0 && odd!=2)
        return 0;
    int k=findSet(1);
    for(int i=2;i<=tot;i++)
        if(k!=findSet(i))
            return 0;
    return 1;
}

int main(){

    //freopen("input.txt","r",stdin);

    char s1[15],s2[15];
    init();
    root=create();
    while(~scanf("%s%s",s1,s2)){
        int x=SearchTrie(s1);   //映射求编号速度太慢
        int y=SearchTrie(s2);   //用字典树来求编号
        if(x==0)
            InsertTrie(s1,x=++tot);
        if(y==0)
            InsertTrie(s2,y=++tot);
        deg[x]++;
        deg[y]++;
        int fx=findSet(x);
        int fy=findSet(y);
        if(fx!=fy)
            father[fx]=fy;
    }
    if(judge())
        printf("Possible\n");
    else
        printf("Impossible\n");
    return 0;
}