HDU 5676 ztr loves lucky numbers - dblank

# HDU 5676 ztr loves lucky numbers

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(1n105) cases

For each cases:

The only line contains a positive integer n(1n1018). This number doesn't have leading zeroes.

Output
For each cases

Sample Input
2 4500 47

Sample Output
4747 47

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<map>
#include<vector>
#include<cstring>
#include<cmath>
using namespace std;
typedef long long ll;
const int inf =0x3f3f3f3f;
const double  pi = acos(-1.0);
const int N = 1e5 + 10;
ll s[N*5];
int k;
void dfs(ll num, int a, int b)
{
if(a+b == 19)
return ;
if(a == b && a+b)
s[k++] = num;
dfs(num*10 + 4, a+1, b);
dfs(num*10 + 7, a, b+1);
}
int main()
{
int t;
k = 0;
dfs(0, 0, 0);
sort(s, s+k);
cin>>t;
while(t--)
{
ll n;
scanf("%I64d", &n);
int index = lower_bound(s, s+k, n) - s;
if(index == k)
printf("44444444447777777777\n");
else printf("%I64d\n", s[sb]);
}
return 0;
}