Sicily 1935 二叉樹重建

題目要求說的很清楚，給出一個數的先序和中序遍歷結果，構建樹並按照廣度優先輸出。先序遍歷的第一個數即爲根節點，在中序遍歷中找到之後它左面的都是左子孫結點右邊同理。

// Problem#: 1935
// Submission#: 3291146
// The source code is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
// URI: http://creativecommons.org/licenses/by-nc-sa/3.0/
// All Copyright reserved by Informatic Lab of Sun Yat-sen University
#include<iostream>
#include<queue>
#include<string>
using namespace std;
struct Tree {
    char c;
    Tree *left, *right;
};
Tree* build(string pre, string in) {
    Tree *root = NULL;
    if (pre.length() > 0) {
        root = new Tree;
        char ch = pre[0];
        root->c = ch;
        int pos = in.find(ch);
        root->left = build(pre.substr(1, pos), in.substr(0, pos));
        root->right = build(pre.substr(pos + 1), in.substr(pos + 1));
    }
    return root;
}
int main() {
    int n;
    cin >> n;
    while (n--) {
        string pre, in;
        cin >> pre >> in;
        
        Tree *t = build(pre, in);
        queue<Tree*> que;
        que.push(t);
        while (!que.empty()) {
            Tree *temp = que.front();
            que.pop();
            cout << temp->c;
            if (temp->left != NULL) {
                que.push(temp->left);
            }
            if (temp->right != NULL) {
                que.push(temp->right);
            }
        }
        cout << endl;
    }
}