CodeForces 535B — Tavas and SaDDas

原题：http://codeforces.com/problemset/problem/535/B

题意：求1 ~ n中只包含4、7的数有多少个；

#include<stdio.h>
#include<queue>
#include<iostream>
#include<algorithm>

using namespace std;
struct node
{
	long long x;
};
queue<node>q;
int main()
{
	int n;
	while(scanf("%d", &n)!=EOF)
	{
		int con = 0;
		node a;
		a.x = 4;
		q.push(a);
		a.x = 7;
		q.push(a);
		while(!q.empty())
		{
			node b = q.front();
			q.pop();
			if(b.x<=n)
			{
				node c;
				c.x = b.x*10+4;
				q.push(c);
				c.x = b.x*10+7;
				q.push(c);
				con++;
			}
		}
		printf("%d\n", con);
	}
	return 0;
}