HDU 5676

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
   
   
   
   

 

题意：问最小的大于等于n的数，并且这个数只由4和7组成，且4和7的个数一样。

思路：直接将1~16位的所有数通过dfs打表得到，奇数位的n的答案肯定是位数加1的合法的数，但是当n大于16位最大的合法数的时候，答案是爆long long，通过特判输出。

#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 sb = lower_bound(s, s+k, n) - s;
        if(sb == k)
            printf("44444444447777777777\n");
        else printf("%I64d\n", s[sb]);
    }
    return 0;
}