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

 

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 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\n", lower_bound (a+1, a+1+tot, n) - a); 46  } 47 48 return 0; 49 }