Minimal representation of the tree

Tree subway system

#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>

using namespace std;

int n;

// 数的最小表示法，用 01 序列表示子树，然后按照字典序排序
string dfs(string &s, int &u) {
    
    
    // 跳过根节点
    u ++;
    vector<string> seqs;
    while (s[u] == '0') seqs.push_back(dfs(s, u));
    u ++;
    
    sort(seqs.begin(), seqs.end());
    string res = "0";
    for (auto x : seqs) {
    
    
        // cout << x << ' ';
        res += x;
    }
    res += '1';
    return res;
    
}

int main() {
    
    
    cin >> n;
    while (n --) {
    
    
        string sa, sb;
        int ua = 0, ub = 0;
        cin >> sa >> sb;
        // 给树加上一个根节点
        sa = '0' + sa + '1';
        sb = '0' + sb + '1';
        if (dfs(sa, ua) == dfs(sb, ub)) puts("same"); 
        else puts("different");
    }
    return 0;
}