POJ 2513 Colored Sticks（欧拉回路，字典树，并查集）

view code//第一次用指针写trie,本来是用二维数组，发现数组开不下，只好删删改改，改成指针
//做这道题，知道了欧拉回路判定，还有用指针写trie
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
const int N = 500010;
char s1[15], s2[15];
int fa[N], u, v, in[N], color =1;

struct Trie
{
    Trie *ch[26];
    int val;
    void init()
    {
        for(int i=0; i<26; i++) ch[i] = NULL;
        val = 0;
    }

    Trie()
    {
        for(int i=0; i<26; i++) ch[i] = NULL;
        val = 0;
    }

    int idx(char c){return c-‘a‘; }

    int ins_find(char *s, Trie *t)
    {
        int  n = strlen(s);
        for(int i=0; i<n; i++)
        {
            int c = idx(s[i]);
            if(!t->ch[c])
            {
                t->ch[c] = new Trie();
            }
            t = t->ch[c];
        }
        if(!t->val) t->val = color++;
        return t->val;
    }
}*tr;

int find(int x)
{
    if(fa[x]<0) return x;
    return fa[x]=find(fa[x]);
}


int main()
{
//    freopen("in.txt", "r", stdin);
    memset(fa, -1, sizeof(fa));
    tr = new Trie();
    while(scanf("%s%s", s1, s2)>0)
    {
        u = tr->ins_find(s1, tr), v = tr->ins_find(s2, tr);
        in[u]++, in[v]++;
        u = find(u), v = find(v);
        if(u!=v) fa[u] = v;
    }
    int num1=0, num2=0;

    for(int i=1; i<color; i++)
    {
        if(in[i]&1) num1++;
        if(fa[i]==-1) num2++;
    }
    if((num1==0 || num1==2) && num2<2)
        puts("Possible");
    else puts("Impossible");
    return 0;
}