POJ 2513 Colored Sticks 字典树、并查集、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

#include <stdio.h>

#include <iostream>

using namespace std;



int id = 0, par[500010], degree[500010] = {0};



int find_set(int x)

{

    return par[x] != x ? par[x] = find_set(par[x]) : x;

}



struct Trie_node

{

    int flag, id;

    struct Trie_node *next[26];

    Trie_node()

    {

        for(int i = 0; i < 26; i++)

            next[i] = NULL;

        flag = 0;

    }

};



int trie_insert(struct Trie_node *p, char s[])

{

    for(int i = 0; s[i]; i++)

    {

        if(p->next[s[i]-'a'] == NULL)

            p->next[s[i]-'a'] = new Trie_node;

        p = p->next[s[i]-'a'];

    }

    if(p->flag != 1)

    {

        p->flag = 1;

        p->id = ++id;

    }

    return p->id;

}



bool check()

{

    int x = find_set(1);

    for(int i = 2; i <= id; i++)

    {

        if(find_set(i) != x)

            return 0;

    }

    int degree_odd = 0;

    for(int i = 1; i <= id; i++)

    {

        if(degree[i] & 1)

            degree_odd++;

    }

    return (degree_odd == 1 || degree_odd > 2) ? 0 : 1;

}



int main()

{

    for(int i = 0; i <= 500000; i++)

        par[i] = i;

    struct Trie_node *root = new Trie_node;

    char s1[12], s2[12];

    while(scanf("%s %s", s1, s2) != EOF)

    {

        int x = trie_insert(root, s1);

        int y = trie_insert(root, s2);

        degree[x]++;

        degree[y]++;

        int fx = find_set(x);

        int fy = find_set(y);

        if(fx != fy)

            par[fx] = fy;

    }

    printf("%s\n", check() ? "Possible" : "Impossible");

    return 0;

}

View Code