二叉树建立

前序 + 中序

#include<iostream>
#include<deque>
using namespace std;

deque<int> rear,center,pref;

void build(deque<int> pre,deque<int> cen){
    int temp;
    if(pre.size()) temp = pre.front();
    else return;

    int pos;
    for(int i = 0;i < cen.size();i ++){
        if(cen[i] == pre.front()){
            pos = i;
            break;
        }
    }

    pre.pop_front();

    deque<int> p,c;
    p.assign(pre.begin(),pre.begin() + pos);
    c.assign(cen.begin(),cen.begin() + pos);
    build(p,c);

    p.clear(),c.clear();
    p.assign(pre.begin() + pos,pre.end());
    c.assign(cen.begin() + pos + 1,cen.end());
    build(p,c);

    rear.push_back(temp);
}

int main(){
    int n;
    cin >> n;

    for(int i = 0;i < n * 2;i ++){
        int t;
        cin >> t;

        if(i < n) center.push_back(t);
        else pref.push_back(t);
    }

    build(pref,center);

    for(auto i : rear) cout << i << ' ';
}

中序 + 后序

#include<iostream>
#include<vector>

using namespace std;

const int N = 50;

vector<int> rear;
vector<int> center;
vector<int> pre;

int n;

void build(vector<int> re,vector<int> cen){
    if(re.size()) pre.push_back(re.back());
    else return;

    int pos;
    for(int i = 0;i < cen.size();i ++){
        if(cen[i] == re.back()){
            pos = i;
            break;
        }
    }
    
    re.pop_back();

    vector<int> r,c;
    r.assign(re.begin(),re.begin() + pos);
    c.assign(cen.begin(),cen.begin() + pos);
    build(r,c);

    r.clear(),c.clear();
    r.assign(re.begin() + pos,re.end());
    c.assign(cen.begin() + pos + 1,cen.end());
    build(r,c);
}

int main(){
    cin >> n;

    for(int i = 0;i < n * 2;i ++){
        int t;
        cin >> t;

        if(i < n) rear.push_back(t);
        else center.push_back(t);
    }

    build(rear,center);

    cout << "Preorder:";
    for(auto i : pre) cout << ' ' << i;
}

cite

按层次遍历

#include<iostream>
#include<deque>
#include<cstring>
#include<vector>

using namespace std;

deque<int> rear,center,pref;
int tr[100010];
vector<int> alls[1010];
int dep = 0;


void build(deque<int> pre,deque<int> cen,int u){
    if(pre.size()) tr[u] = pre.front();
    else return;

    int pos;
    for(int i = 0;i < cen.size();i ++){
        if(cen[i] == pre.front()){
            pos = i;
            break;
        }
    }

    pre.pop_front();

    deque<int> p,c;
    p.assign(pre.begin(),pre.begin() + pos);
    c.assign(cen.begin(),cen.begin() + pos);
    build(p,c,u << 1);

    p.clear(),c.clear();
    p.assign(pre.begin() + pos,pre.end());
    c.assign(cen.begin() + pos + 1,cen.end());
    build(p,c,u << 1 | 1);
}

void print(int u,int de){
    if(tr[u] != -1) alls[de].push_back(tr[u]),dep = max(dep,de);
    else return;

    print(u << 1 | 1,de + 1),print(u << 1,de + 1);
}

int main(){
    memset(tr,-1,sizeof tr);
    int n;
    cin >> n;

    for(int i = 0;i < n * 2;i ++){
        int t;
        cin >> t;

        if(i < n) center.push_back(t);
        else pref.push_back(t);
    }

    build(pref,center,1);

    print(1,0);

    for(int i = 0;i <= dep;i ++){
        for(auto j : alls[i]) cout << (i ? " " : "") << j; 
    }
}