CCNUOJ 1010 The Almost Lucky Numbers

1010: The Almost Lucky Numbers

Time Limit: 1 Sec  Memory Limit: 128 MB
Submit: 16  Solved: 11
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Description

John and Brus believe that the digits 4 and 7 are lucky and all others are not. According to them, an almost lucky number is a number that contains at most one non-lucky digit in its decimal representation. Return the total number of almost lucky numbers between a and b, inclusive.

Input

Each line contains two integers a,b<=1,000,000

Output

For each line of input,output the total number of almost lucky numbers between a and b, inclusive.

Sample Input

4 7 8 19

Sample Output

4 4

思路：数据不大，直接搜即可。或者另一种方法，排列组合，不成熟，当搜索的数和当前数位数相同的时候没想出来怎么算

#include<stdio.h>
int l(int x)
{
	int cnt(0);
	while(x>0) {x/=10;cnt++;}
	return cnt;
}
bool is(int x)
{
	bool y(true);
	while(x>0)
	{
		if(!(x%10==4||x%10==7)) 
		{if(y) y=!y;else return false;}
		x/=10;
	}
	return true;
}
int main()
{
	int x,y,t,i,a,lx,ly;
	int e[9],u[9];
	e[0]=1;u[0]=1;e[1]=1;
	for(i=1;i<9;i++)
	{
		u[i]=u[i-1]*2;
	}
	for(i=2;i<9;i++)
	{
		e[i]=e[i-1]*10;
	}
	while(scanf("%d%d",&x,&y)==2)
	{
		a=0;
		if(x>y) {t=x;x=y;y=t;}
		lx=l(x);ly=l(y);
		if(ly-lx>=2)
		{
			for(i=lx+1;i<=ly-1;i++)
			{
				a+=u[i]+8*u[i-1]*i-u[i-1];
			}
			for(i=x;i<e[lx+1];i++)
			{
				if(is(i)) a++;
			}
			for(i=e[ly];i<=y;i++)
			{
				if(is(i)) a++;
			}
		}
		else
		{
			for(i=x;i<=y;i++)
			{
				if(is(i)) a++;
			}
		}
		printf("%d\n",a);
	}
	return 0;
}