hdu 5676 ztr loves lucky numbers

ztr loves lucky numbers

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

Total Submission(s): 1112    Accepted Submission(s): 468


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
4000
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

 
   首先找出所有的幸运数字，再进行查找

   例如47 74 4477 4747 4774 7447 7474 7744.........

  用dfs枚举即可，再存放在set中，用lower_bound查找第一个不小于输入数字的元素。

  当输入大于 777777777444444444时，满足条件的下一个幸运数超出long long 的范围，所以要特判。#include <iostream>
#include <cstdio>
#include <set>
using namespace std;
typedef long long ll;
ll a[262220];
set<ll>b;
void dfs(ll x,ll y,ll cnt)
{
if(x==0&&y==0)
{
b.insert(cnt);
return;
}
if(x>0) dfs(x-1,y,cnt*10+4);
if(y>0) dfs(x,y-1,cnt*10+7);
}
int main()
{
int t;
b.insert(47);
b.insert(74);
for(int i=2;i<=9;i++)
{
dfs(i,i,0);
}
scanf("%d",&t);
ll n;
while(t--)
{
scanf("%lld",&n);
if(n>777777777444444444)
{
printf("44444444447777777777\n");
continue;
}
printf("%lld\n",*b.lower_bound(n));
}
return 0;
}