打卡 代码写的有点乱 思路表述不清晰 但终究是做出来了 花了不少时间

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define N 100

int n;

char layer[N] = "";
char mid[N] = "";
char ans[N] = "";

typedef struct Free
{
    char value;
    struct Free* left;//左节点
    struct Free* right;//右节点
}Free;

void fun(int la, int rear, int front, Free* now)
{
    now->value = layer[la];
    now->left = NULL;
    now->right = NULL;
    if (la == n - 1) return;
    for (int i = la + 1;i < n;i++)
    {
        if (mid[layer[i]] < mid[layer[la]] && mid[layer[i]] >= rear && mid[layer[i]] <= front && now->left == NULL)
        {
            Free* left = (Free*)malloc(sizeof(Free));
            now->left = left;
            fun(i, rear, mid[layer[la]], left);
        }
        if (mid[layer[i]] > mid[layer[la]] && mid[layer[i]] >= rear && mid[layer[i]] <= front )
        {
            Free* right = (Free*)malloc(sizeof(Free));
            now->right = right;
            fun(i, mid[layer[la]], front, right);
            return;
        }
    }
}

void Print(Free* now)
{
    cout << now->value;
    if (now->left != NULL) Print(now->left);
    if (now->right != NULL) Print(now->right);
    free(now);
}

int main()
{
    cin >> mid >> layer;
    n = strlen(mid);
    for (int i = 0;i < n;i++) mid[mid[i]] = i;
    Free* head = (Free*)malloc(sizeof(Free));
    head->left = NULL;
    head->right = NULL;
    fun(0, 0, n - 1, head);
    Print(head);
    return 0;
}