欧拉回路
https://www.cnblogs.com/acxblog/p/7390301.html
luogu p2731
1 #include<bits/stdc++.h> 2 using namespace std; 3 4 const int N=510,M=2*1100; 5 struct node{ 6 int x,y,next; 7 bool bk; 8 }a[M]; 9 int n,al,ql,first[N],degree[N],q[N]; 10 11 void ins(int x,int y) 12 { 13 a[++al].x=x;a[al].y=y;a[al].bk=1; 14 a[al].next=first[x];first[x]=al; 15 } 16 17 void dfs(int x) 18 { 19 // printf("x = %d\n",x); 20 int nxt=n+1,id=0; 21 for(int i=first[x];i;i=a[i].next) 22 { 23 int y=a[i].y; 24 if(!a[i].bk) continue; 25 if(y<nxt) nxt=y,id=i; 26 } 27 if(id) 28 { 29 a[id].bk=0; 30 a[(id&1) ? id+1 : id-1].bk=0; 31 dfs(nxt); 32 } 33 q[++ql]=x; 34 } 35 36 int main() 37 { 38 //freopen("a.in","r",stdin); 39 int m; 40 scanf("%d",&m); 41 al=0; 42 memset(first,0,sizeof(first)); 43 memset(degree,0,sizeof(degree)); 44 n=0; 45 for(int i=1;i<=m;i++) 46 { 47 int x,y; 48 scanf("%d%d",&x,&y); 49 n=max(n,max(x,y)); 50 ins(x,y);ins(y,x); 51 degree[x]++;degree[y]++; 52 } 53 int st=n+1; 54 for(int i=1;i<=n;i++) 55 { 56 if(degree[i]&1) st=min(st,i); 57 } 58 if(st==n+1) st=1; 59 ql=0; 60 dfs(st); 61 for(int i=ql;i>=1;i--) printf("%d ",q[i]);printf("\n"); 62 return 0; 63 }
