#include <stdio.h>#include <string.h>#define N 20005struct edge{ int y,next;}e[100005<<1];int first[N],dfn[N],order = 0;int n,m,top;void add(int x,int y){ e[top].y = y; e[top].next = first[x]; first[x] = top++;}int dfs(int x){ int i,y,w,v = -1; dfn[x] = ++order; for(i = first[x];i!=-1;i=e[i].next){ y = e[i].y; if(!dfn[y]){ w = dfs(y); if(w!=-1) printf("%d %d %dn",x,y,w); else{ if(v!=-1){ printf("%d %d %dn",v,x,y); v = -1; }else v = y; } }else if(dfn[x] < dfn[y]){ if(v!=-1){ printf("%d %d %dn",v,x,y); v = -1; }else v = y; } } return v;}int main(){ int i,a,b; top = 0; memset(dfn,0,sizeof(dfn)); memset(first,-1,sizeof(first)); scanf("%d %d",&n,&m); for(i = 0;i<m;i++){ scanf("%d %d",&a,&b); add(a,b); add(b,a); } dfs(1); return 0;}
