DFS Codeforces Round #299 (Div. 2) B. Tavas and SaDDas

 1 /*
 2     DFS：按照长度来DFS，最后排序
 3 */
 4 #include <cstdio>
 5 #include <algorithm>
 6 #include <cstring>
 7 #include <iostream>
 8 #include <cmath>
 9 #include <vector>
10 using namespace std;
11 
12 const int MAXN = 1e3 + 10;
13 const int INF = 0x3f3f3f3f;
14 int b[2] = {4, 7};
15 int a[MAXN];
16 int tot;
17 
18 void DFS(int now, int l, int len)
19 {
20     if (l == len)    {a[++tot] = now;    return ;}
21     for (int i=0; i<2; ++i)
22     {
23         int tmp = now * 10 + b[i];
24         DFS (tmp, l + 1, len);
25     }
26 }
27 
28 void solve(void)
29 {
30     tot = 0;
31     for (int i=1; i<=9; ++i)
32     {
33         DFS (0, 0, i);
34     }
35     sort (a+1, a+1+tot);
36     //for (int i=1; i<=tot; ++i)    printf ("%d ", a[i]);
37 }
38 
39 int main(void)        //Codeforces Round #299 (Div. 2) B. Tavas and SaDDas
40 {
41     solve ();
42     int n;
43     while (scanf ("%d", &n) == 1)
44     {
45         printf ("%d
", lower_bound (a+1, a+1+tot, n) - a);
46     }
47 
48     return 0;
49 }
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