CodeForces 686C-Robbers' watch

题意：
　　一个电子手表的示数是7进制的,现在告诉你一天有多少小时和一小时有多少分钟,问你一天里有多少个时刻,这个表上显示的数字各不相同.

分析：
　　先找出表上有多少位数字,再按位dfs,看最后得到的数是否<n和<m,把分和时转化为7进制,若位数大于7则直接输出0,若不大于零,则用dfs找到分和时的所有位不相同的情况

代码如下：

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <fstream>
 #include <ctime>
 #include <cmath>
 #include <cstdlib>
 #include <algorithm>
 #include <set>
 #include <map>
 #include <list>
 #include <stack>
 #include <queue>
 #include <iterator>
 #include <vector>

 using namespace std;

 #define LL long long
 #define INF 0x3f3f3f3f
 #define MOD 1000000007
 #define MAXN 10000010
 #define MAXM 1000010

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <fstream>
 #include <ctime>
 #include <cmath>
 #include <cstdlib>
 #include <algorithm>
 #include <set>
 #include <map>
 #include <list>
 #include <stack>
 #include <queue>
 #include <iterator>
 #include <vector>

 using namespace std;

 #define LL long long
 #define INF 0x3f3f3f3f
 #define MOD 1000000007
 #define MAXN 10000010
 #define MAXM 1000010

 LL n, m;
 int weishu_n, zongweishu_n_m, kinds_ans;
 int a[];

 int check()
 {
     int sum , x;
     sum = ;
     x = ;
     for(int i = weishu_n-; i >= ; i--)
     {
         sum += x*a[i];
         x *= ;
     }
     if(sum >= n)
         return ;
     sum = ;
     x = ;
     for(int i = zongweishu_n_m-; i >= weishu_n; i--)
     {
         sum += x*a[i];
         x *= ;
     }
     if(sum >= m)
         return ;
     return ;
 }

 void dfs(int cnt)
 {
     if(cnt == zongweishu_n_m)
     {
         if(check())
             kinds_ans++;
     }
     else
         for(int i = ; i < ; i++ )
         {
             int ok = ;
             for(int j = ; j < cnt; j++ )
                 if(i == a[j])
                 {
                     ok = ;
                     break;
                 }
             if(ok)
             {
                 a[cnt] = i;
                 dfs(cnt+);
             }
         }
 }

 int main()
 {
     int pos;
     int kn, km;
     while(scanf("%lld%lld", &n, &m)==)
     {
         memset(a, , sizeof(a));
         kinds_ans = ;
         weishu_n = ;
         zongweishu_n_m = ;
         pos = ;
         kn = n-;
         if(!kn)
             pos++;
         while(kn)
         {
             kn /= ;
             pos++;
         }
         weishu_n = pos;
         km = m-;
         if(!km)
             pos++;
         while(km)
         {
             km /= ;
             pos++;
         }
         zongweishu_n_m = pos;
         dfs();
         if(zongweishu_n_m > )
             printf("0\n");
         else
             printf("%d\n", kinds_ans);
     }

     return ;
 }