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;
}