POJ-2513-Colored Sticks

Colored Sticks

Time Limit: 5000MS		Memory Limit: 128000K
Total Submissions: 35039		Accepted: 9155

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(小写字母) 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.

n根木棒，木棒两端都有颜色，判断能不能把木棒合并成一条，接触的木棒端必须是相同颜色的。
给定一些木棒，木棒两端都涂上颜色，求是否能将木棒首尾相接，连成一条直线，要求不同木棒相接的一边必须是相同颜色的。

欧拉回路判断能否连通

并查集判断是否连成一条

字典树存储颜色

#include<iostream>
#include<string.h>
#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
const int MAX = 500010;
int pre[MAX], cnt = 0, color[MAX];
struct node
{
    int data;
    struct node *next[26];
}*root;
int Search(char *s)
{
    node *p = root;
    for(int i = 0; s[i]; ++i)
    {
        int t = s[i]-'a';
        if(p->next[t]!=NULL)p = p->next[t];
        else return 0;
    }
    return p->data;
}
struct node *creat()
{
    node *p = new node;
    for(int i = 0;i<26;++i)
        p->next[i] = NULL;
    return p;
};
void add(char *s, int x)
{
    node *p = root;
    for(int i = 0; s[i];++i)
    {
        int t = s[i]-'a';
        if(p->next[t]==NULL)
            p->next[t] = creat();
        p = p->next[t];
    }
    p->data =x;
}
int Find(int x)
{
    if(x != pre[x])
    {
        pre[x] = Find(pre[x]);
    }
    return pre[x];
}
bool Judge()
{
    int p = 0;
    for(int i = 1;i<=cnt;++i)
    {
        if(color[i]%2==1)++p;
    }
    if(p!=2&&p!=0)return false;
    p = Find(1);
    for(int i =2; i<=cnt;++i)
    {
        if(p!=Find(i))return false;
    }
    return true;
}
int main()
{
    for(int i = 0; i<MAX; ++i)
        pre[i] = i;
    memset(color, 0, sizeof(color));
    char str1[15], str2[15];
    root = creat();
    while(scanf("%s %s", str1, str2) != EOF)
    {
        int a = Search(str1), b = Search(str2);
        if(a==0)
            add(str1, a = ++cnt);
        if(b==0)
            add(str2, b = ++cnt);
        color[a]++;
        color[b]++;
        int aa = Find(a), bb = Find(b);
        if(aa!=bb)pre[aa] = bb;
    }
    if(Judge())printf("Possible\n");
    else printf("Impossible\n");
    return 0;
}