【字典树+并查集】 poj2513 Colored Sticks

Colored Sticks

http://poj.org/problem?id=2513

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

题意：有很多根木棒，木棒的两端分别涂有颜料，如果端口的颜色相同，则这两个端口可以结合在一起，问给出的木棒能不能连成一条线。

题解：看这个题目很容易就联想到图，经过每条边有且仅有一次，即有欧拉路径。而有欧拉路径就表明图中所有点的度数要么全是偶数，要么只有两个点的度数是奇数。

通过字典树给每个颜色一个编号，利用并查集判断这个是不是一个连通图。

#include<cstdio>
#include<cstring>
using namespace std;
struct node
{
    int next[10];
    int id;
}head[100005];
bool flag;
int cnt;
char s[10005][15];
void build(char *t,int idx,int id)
{
    int len=strlen(t),k;
    for(int i=0;i<len;++i)
    {
        k=t[i]-'0';
        if(head[idx].next[k]==0)
           head[idx].next[k]=(cnt++);
        if((head[idx].id)&&(head[idx].id!=id))
            flag=false;
        idx=head[idx].next[k];
    }
    head[idx].id=id;
}
int main()
{
    int cas,n;
    scanf("%d",&cas);
    for(;cas--;)
    {
        flag=true;
        cnt=1;
        scanf("%d",&n);
        memset(head,0,sizeof(head));
        for(int i=1;i<=n;++i)
        {
            scanf("%s",s[i]);
            build(s[i],0,i);
        }
        if(flag==false)
        {
            puts("NO");
            continue;
        }
        for(int i=1;i<=n;++i)
        {
            build(s[i],0,i);
            if(flag==false) break;
        }
        if(flag) puts("YES");
        else     puts("NO");
    }
    return 0;
}