模板-树的遍历(先序）

#include<bits/stdc++.h>using namespace std;const int maxn=100005;struct Tree{int fa;int l;int r;}tr[maxn];void dfs(int x);int a,b;int n,m;int EA;int main(){cin>>n>>m;for(int i=1;i<=m;i++){cin>>a>>b;if(tr[a].l)tr[a].r=b;elsetr[a].l=b;tr[b].fa=a;}//for//建树for(int i=1;i<=n;i++){if(tr[i].fa==0)EA=i;}//fordfs(EA);return 0;}//mainvoid dfs(int x){cout<<x<<" ";//cout<<tr[x].fa;if(tr[x].l==0&&tr[x].r==0)return;if(tr[x].l)dfs(tr[x].l);//if判断，否则输出0if(tr[x].r) dfs(tr[x].r);}