HDU 1226（超级密码）

广搜题，余数定理：(m+k)%n == (m%n+k)%n

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
#include <string>
#include <algorithm>
using namespace std;
const int INF = 0x3f3f3f3f;

int N, C, M; //输入
bool digit[20]; //数字是否能使用
bool vis[5005]; //访问数组

//字符串s表示的数对N取余
int mod(string s)
{
    int temp = 0;
    for (int i = 0; i < s.size(); i++)
    {
        temp = (temp * C + (int)s[i]) % N;
    }
    return temp;
}

//输出字符串s表示的数
void output(string s)
{
    for (int i = 0; i < s.size(); i++)
    {
        printf("%X", (int)s[i]);
    }
    cout << endl;
}

//广搜
bool bfs()
{
    queue<string> q;
    string a, b;
    for (int i = 1; i <= 15; i++)
    {
        if (digit[i])
        {
            a = (char)i;
            if (mod(a) == 0)
            {
                output(a);
                return false;
            }
            q.push(a);
        }
    }
    while (!q.empty())
    {
        a = q.front();
        q.pop();
        for (int i = 0; i <= 15; i++)
        {
            if (digit[i] && a.size() + 1 <= 500)
            {
                b = a + (char)i;
                int rem = mod(b);
                if (rem == 0)
                {
                    output(b);
                    return false;
                }
                else
                {
                    if (vis[rem] == 0)
                    {
                        vis[rem] = 1;
                        q.push(b);
                    }
                }
            }
        }
    }
    return true;
}

int main()
{
    int T;
    cin >> T;
    while (T--)
    {
        memset(digit, 0, sizeof(digit));
        memset(vis, 0, sizeof(vis));
        cin >> N >> C >> M;
        int num; //能使用的数字
        for (int i = 0; i < M; i++)
        {
            scanf("%x", &num); //需要十六进制读取输入
            digit[num] = true;
        }
        if (N == 0)
        {
            if (digit[0])
                cout << 0 << endl;
            else
                cout << "give me the bomb please" << endl;
            continue;
        }
        if (bfs())
            cout << "give me the bomb please" << endl;
    }
    return 0;
}