PDD笔试题：最小字符串

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直接递归即可

需要注意的地方是set是有序的，所以DFS得到第一个结果one就是最终答案

代码如下：

#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <string>
#include <climits>
#include <algorithm>
#include <sstream>
#include <functional>
#include <bitset>
#include <numeric>
#include <cmath>
#include <regex>
#include <cstdlib>

using namespace std;

string res="";

bool dfs(vector<set<char>>& dict, set<string> all, int index, string one)
{
    if (index == dict.size())
    {
        if (all.find(one) == all.end())
        {
            res = one;
            return true;
        }
        return false;
    }
    else
    {
        for (char i : dict[index])
        {
            bool tmp = dfs(dict, all, index + 1, one + i);
            if (tmp == true)
                return true;
        }
        return false;
    }
}

int main()
{
    int n, l;
    cin >> n >> l;
    vector<string> all(n, "");
    for (int i = 0; i < n; i++)
        cin >> all[i];
    vector<set<char>> dict(l, set<char>());
    for (int i = 0; i < l; i++)
    {
        for (string one : all)
            dict[i].insert(one[i]);
    }

    set<string> t(all.begin(), all.end());
    dfs(dict, t, 0, "");
    if (res.length()<=0)
        cout << "-" << endl;
    else
        cout << res << endl;

}