PKU 2513 Colored Sticks

trie树+并查集+欧拉回路

用trie树将字符串一一映射（貌似用hash也行）， 用并查集判断图是否联通，然后判断是否存在欧拉回路（不要以为回路不符合题意，其实只要拉直就好了），即度为奇数的点有两个或没有。

#include <stdio.h>

const int N = 250000 + 5;

int fa[N*2]={0};

int num;

struct Node{

Node *branch[26];

int key;

Node(){

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

branch[i] = NULL;

key = 0;

}

} *root;

void NewNode( Node *point, int cnum )

{

Node *nnode = new Node();

point->branch[cnum] = nnode;

}

int insert( char *word )

{

Node *point = root;

while ( *word!='/0' )

{

int cnum = *word-'a';

if ( point->branch[cnum] == NULL )

NewNode( point , cnum );

point = point->branch[cnum];

word ++;

}

if ( point->key==0 )

{

point->key = ++num;

fa[num-1] = num-1;

}

return point->key;

}

int v[N*2] = {0};

int Root( int x)

{

int r = fa[x];

if ( r!=x )

fa[x] = Root( r );

return fa[x];

}

int main ()

{

num = 0;

root = new Node();

int t1, t2;

char s1[15], s2[15];

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

{

t1 = insert( s1 );

t2 = insert( s2 );

int ra = Root( t1-1 );

int rb = Root( t2-1 );

if ( ra!=rb )

fa[rb] = ra;

v[t1-1]++;

v[t2-1]++;

}

int nodd = 0;

int rr = Root( 0 );

int flag = 1;

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

{

if ( v[i]%2==1 )

nodd ++;

if ( Root(i)!=rr )

{

flag = 0;

break;

}

}

if ( ( nodd==0 || nodd==2 ) && flag )

printf("Possible/n");

else

printf("Impossible/n");

return 0;

}