POJ-2513 Colored Sticks 欧拉回路
题目链接：http://poj.org/problem?id=2513
建立无向图，看图是否存在欧拉道路。首先判断图是否连通，可以用并查集或者一遍BFS判断，最后判断入度数就可以了。
1 //STATUS:C++_AC_1266MS_79348KB 2 #include<stdio.h> 3 #include<stdlib.h> 4 #include<string.h> 5 #include<math.h> 6 #include<iostream> 7 #include<string> 8 #include<algorithm> 9 #include<vector> 10 #include<queue> 11 #include<stack> 12 #include<map> 13 using namespace std; 14 #define LL __int64 15 #define pii pair<int,int> 16 #define Max(a,b) ((a)>(b)?(a):(b)) 17 #define Min(a,b) ((a)<(b)?(a):(b)) 18 #define mem(a,b) memset(a,b,sizeof(a)) 19 #define lson l,mid,rt<<1 20 #define rson mid+1,r,rt<<1|1 21 const int N=510000,INF=0x3f3f3f3f,MOD=1999997; 22 const LL LLNF=0x3f3f3f3f3f3f3f3fLL; 23 24 struct Node{ 25 int u,v; 26 }e[N]; 27 struct Trie{ 28 Trie(){mem(next,0);val=0;} 29 Trie *next[26]; 30 int val; 31 }; 32 int num[N],first[N],next[N],vis[N]; 33 int cou,m; 34 35 void adde(int a,int b) 36 { 37 e[m].u=a,e[m].v=b; 38 next[m]=first[a],first[a]=m++; 39 e[m].u=b,e[m].v=a; 40 next[m]=first[b],first[b]=m++; 41 } 42 43 int bfs() 44 { 45 int i,u,v,k=1; 46 queue<int> q; 47 q.push(1); 48 mem(vis,0); 49 vis[1]=1; 50 while(!q.empty()){ 51 u=q.front();q.pop(); 52 for(i=first[u];i!=-1;i=next[i]){ 53 if(!vis[e[i].v]){ 54 vis[e[i].v]=1; 55 q.push(e[i].v); 56 k++; 57 } 58 } 59 } 60 return k==cou; 61 } 62 63 int build(Trie *rt,char *a) 64 { 65 if(*a==0){ 66 if(rt->val)num[rt->val]++; 67 else { 68 rt->val=++cou; 69 num[cou]++; 70 } 71 return rt->val; 72 } 73 int idx=*a-'a'; 74 if(!rt->next[idx]) 75 rt->next[idx]=new Trie; 76 return build(rt->next[idx],a+1); 77 } 78 79 int main() 80 { 81 // freopen("in.txt","r",stdin); 82 int i,j,ok,a,b; 83 char s1[15],s2[15]; 84 Trie *head; 85 head=new Trie; 86 m=cou=0; 87 mem(num,0);mem(first,-1); 88 while(~scanf("%s%s",s1,s2)){ 89 a=build(head,s1); 90 b=build(head,s2); 91 adde(a,b); 92 } 93 ok=0; 94 for(i=1;i<=cou;i++){ 95 if(num[i]&1)ok++; 96 if(ok>2)break; 97 } 98 printf("%s\n",(!cou || ((ok==2 || ok==0) && bfs()))?"Possible":"Impossible"); 99 return 0; 100 }
