【欧拉回路】P1341 无序字母对

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

bool edge[127][127];
int n;
int h;
string ans;
int d[127];

void dfs(int node)
{
    for (int i = 'A'; i <= 'z'; i++)
    {
        if (edge[node][i])
        {
            edge[node][i] = edge[i][node] = false;
            dfs(i);
            if (i == 'Z') i = 'a' - 1;
        }
    }
    ans.push_back(node);
}

int main()
{
    cin >> n;
    string t;
    for (int i = 0; i < n; i++)
    {
        cin >> t;
        edge[t[0]][t[1]] = true;
        edge[t[1]][t[0]] = true;
        d[t[0]]++;
        d[t[1]]++;
    }
    int cnt = 0;
    for (int i = 'A'; i <= 'z'; i++)
    {
        if (d[i] % 2)
        {
            if(!h) h = i;
            cnt++;
        }
        if (i == 'Z') i = 'a' - 1;
        //cout << cnt << " ";
    }
    if (cnt && cnt != 2)
    {
        cout << "No Solution";
        return 0;
    }
    if(!h)
        for (int i = 'A'; i <= 'z'; i++)
        {
            if (d[i])
            {
                h = i;
                break;
            }
            if (i == 'Z') i = 'a' - 1;
        }
    dfs(h);
    //cout << ans.length();
    for (int i = ans.length() - 1; i >= 0; i--)
    {
        cout << ans[i];
    }
}