PTA L2-011 Playing with Binary Tree (25 points)

Given the pre-order and middle-order sequences of the binary tree, the binary tree is reconstructed. As for the level traversal, it is only necessary to enter the right subtree on the binary tree after the reconstruction is completed.

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <cmath>
#include <string>
#include <vector>
#include <stack>
#include <map>
#include <sstream>
#include <cstring>
#include <set>
#include <cctype>
#include <bitset>
#define IO                       \
    ios::sync_with_stdio(false); \
    // cin.tie(0);                  \
    // cout.tie(0);
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int maxn = 1e5 + 100;
const int maxm = 1e6 + 10;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int inf = 0x3f3f3f3f;
const LL mod = 1e9 + 7;
int dis[8][2] = {0, 1, 1, 0, 0, -1, -1, 0, 1, -1, 1, 1, -1, 1, -1, -1};
struct Node
{
    int num;
    Node *left;
    Node *right;
};
int mid[40], pre[40];
int n;
Node *creat(int mid[], int pre[], int n)
{
    if (n <= 0)
        return NULL;
    int *p = mid;
    while (p)
    {
        if (*p == *pre)
            break;
        p++;
    }
    Node *T = new Node;
    T->num = *p;
    int len = p - mid;
    T->left = creat(mid, pre + 1, len);
    T->right = creat(p + 1, pre + len + 1, n - len - 1);
    return T;
}
void Level(Node *T)
{
    queue<Node *> q;
    q.push(T);
    int flag = 0;
    while (!q.empty())
    {
        Node *a = q.front();
        q.pop();
        if (flag == 0)
        {
            cout << a->num;
            flag = 1;
        }
        else
        {
            cout << " " << a->num;
        }
        if (a->right)
            q.push(a->right);
        if (a->left)
            q.push(a->left);
    }
    return;
}
int main()
{
#ifdef ONLINE_JUDGE
#else
    freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
#endif
    int n;
    cin >> n;
    for (int i = 0; i < n; i++)
        cin >> mid[i];
    for (int i = 0; i < n; i++)
        cin >> pre[i];
    Node *T;
    T = creat(mid, pre, n);
    Level(T);
    return 0;
}