CF 96B_Lucky Numbers (easy) (DFS)

wyh — Wed, 03 Aug 2011 06:13:00 GMT

题目大意：给出一个数字，求不小于它且由4，7两个数字组成，4跟7的出现次数要一样多。

思路：DFS
每次递归累计4，7出现的个数，直到满足题意即可。
注意要long long

代码：

1#include <iostream>
2#include <cstdio>
3#include <cstring>
4#include <string>
5#include <cmath>
6#include <algorithm>
7
8using namespace std;
9
10long long  n,res;
11
12void dfs(long long x,int four,int seven)
13{
14   if(x>1000000000000)
15       return;
16   if(x>=n&&four==seven)
17   {
18       if(res==0||res>x)
19            res=x;
20   }
21    dfs(x*10+4,four+1,seven);
22    dfs(x*10+7,four,seven+1);
23}
24
25int main()
26{
27   while(~scanf("%I64d",&n))
28   {
29        res=0;
30        dfs(4,1,0);
31        dfs(7,0,1);
32        printf("%I64d\n",res);
33   }
34   return 0;
35}
36

wyh 2011-08-03 14:13 发表评论

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CF 96B_Lucky Numbers (easy) (DFS)