hdu 5676 ztr loves lucky numbers（BC——暴力打表+二分查找）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=5676

ztr loves lucky numbers

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)

Total Submission(s): 594    Accepted Submission(s): 257

Problem Description

ztr loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn't contain digits other than 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Lucky number is super lucky if it's decimal representation contains equal amount of digits 4 and 7. For example, numbers 47, 7744, 474477 are super lucky and 4, 744, 467 are not.

One day ztr came across a positive integer n. Help him to find the least super lucky number which is not less than n.

 

Input

There are T(1≤n≤105) cases

For each cases:

The only line contains a positive integer n(1≤n≤1018).
This number doesn't have leading zeroes.

 

Output

For each cases

Output the answer

 

Sample Input

2
4500
47

 

Sample Output

4747
47

 

Source

BestCoder Round #82 (div.2)

 

题目大意：

ztr喜欢幸运数字，他对于幸运数字有两个要求
1：十进制表示法下只包含4、7
2：十进制表示法下4和7的数量相等
比如47,474477就是
而4,744,467则不是

现在ztr想知道最小的但不小于n的幸运数字是多少

解题思路：暴力打出所有幸运数~~~~然后二分查找即可。

详见代码。

#include <iostream>
#include <cstdio>

using namespace std;

#define ll long long

ll a[100000];
int k=0;

void dfs(ll ans,int num4,int num7)
{
if (num4==0&&num7==0)
{
a[k++]=ans;
return;
}
if (num4==0)
{
dfs(ans*10+7,num4,num7-1);
}
else if (num7==0)
{
dfs(ans*10+4,num4-1,num7);
}
else
{
dfs(ans*10+4,num4-1,num7);
dfs(ans*10+7,num4,num7-1);
}
}

int main()
{
int t;
scanf("%d",&t);
for (int i=2;i<=18;i+=2)
dfs(0,i/2,i/2);
while (t--)
{
ll n;
scanf("%lld",&n);
if(n>777777777444444444LL)
{
printf("44444444447777777777\n");
continue;
}
int l=0,r=k;
while (r>l)
{
int mid=(l+r)/2;
// cout<<mid<<endl;
if (a[mid]<n)
{
l=mid+1;
}
else
{
r=mid;
}
}
printf("%lld\n",a[r]);
}
return 0;
}