题解 | Problem D

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


struct treenode {
    char data;
    treenode* left = NULL;
    treenode* right = NULL;
};

void postorder(treenode*& root, string pre, string mid) {
    if (pre.empty())return;
    int pos = mid.find(pre[0]);
    root = new treenode;
    root->data = pre[0];
    postorder(root->left, pre.substr(1, pos), mid.substr(0,pos));
    postorder(root->right, pre.substr(pos + 1), mid.substr(pos + 1));
    cout << root->data;
}
int main() {
    string pre, mid;
    while (cin >> pre >> mid) { // 注意 while 处理多个 case
        treenode* root = NULL;
        postorder(root, pre, mid);
        cout<<endl;
    }
}
// 64 位输出请用 printf("%lld")