Codeforces Round #359 (Div. 2) C. Robbers' watch (暴力DFS)

 1 //#pragma comment(linker, "/STACK:102400000, 102400000")
 2 #include <algorithm>
 3 #include <iostream>
 4 #include <cstdlib>
 5 #include <cstring>
 6 #include <cstdio>
 7 #include <vector>
 8 #include <cmath>
 9 #include <ctime>
10 #include <list>
11 #include <set>
12 #include <map>
13 using namespace std;
14 typedef long long LL;
15 typedef pair <int, int> P;
16 const int N = 1e5 + 5;
17 int num[10], n, m, ans;
18 bool vis[10];
19 
20 int get(int num[], int len) {
21     int res = 0, temp = 1;
22     for(int i = len; i >= 1; --i) {
23         res += num[len] * temp;
24         temp *= 7;
25     }
26     return res;
27 }
28 
29 void dfs(int len1, int len2, int dep) {
30     if(dep == len1 + len2) {
31         int sum = 0, temp = 1;
32         for(int i = len1+len2; i >= len1+1; --i) {
33             sum += temp*num[i];
34             temp *= 7;
35         }
36         if(sum < m)
37             ans++;
38         return ;
39     }
40     else if(dep == len1) {
41         int sum = 0, temp = 1;
42         for(int i = len1; i >= 1; --i) {
43             sum += temp*num[i];
44             temp *= 7;
45         }
46         if(sum >= n)
47             return ;
48     }  
49     dep++;
50     for(int i = 0 ; i < 7 ; ++i) {
51         if(vis[i])
52             continue;
53         vis[i] = true;
54         num[dep] = i;
55         dfs(len1, len2, dep);
56         vis[i] = false;
57     }
58 
59 }
60 
61 int main()
62 {
63     cin >> n >> m;
64     int cnt1 = 0, cnt2 = 0, temp = n - 1;
65     do {
66         temp /= 7;
67         ++cnt1;
68     } while(temp);
69     temp = m - 1;
70     do {
71         temp /= 7;
72         ++cnt2;
73     } while(temp);
74     if (cnt1 + cnt2 > 7) {
75         cout << 0 << endl;
76     } else {
77         dfs(cnt1, cnt2, 0);
78         cout << ans << endl;
79     }
80     return 0;
81 }