题解

#include <bits/stdc++.h>
using namespace std;

int l[110],r[110],a[110];
void dfs1(int x) {
    if (x == 0) return;
    cout << a[x] << " ";
    dfs1(l[x]);
    dfs1(r[x]);
}

void dfs2(int x) {
    if (x == 0) return;
    dfs2(l[x]);
    cout << a[x] << " ";
    dfs2(r[x]);
}

void dfs3(int x) {
    if (x == 0) return;
    dfs3(l[x]);
    dfs3(r[x]);
    cout << a[x] << " ";
}

int main(){
    int n;     
    cin >> n;
    for(int i=1;i<=n;i++){
        cin >> a[i];
        if(i==1) continue;
        int j = 1;
        while(true){
                if(a[j]>a[i]){
                    if(l[j]==0) {
                    l[j] = i;
                    break;
                }else{
                    j = l[j];
                }
                }else{
                    if(r[j]==0){
                    r[j] = i;
                    break;
                }else{
                    j = r[j];
                }
                }
            }

    }
    dfs1(1);
        cout << endl;
    dfs2(1);
        cout << endl;
    dfs3(1);


return 0;
}