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

题目链接：

ztr loves lucky numbers

time limit: 2000/1000 ms (java/others)memory limit: 65536/65536 k (java/others)

total submission(s): 594accepted 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 integern(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 (p.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 
#include 

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;i777777777444444444ll)
        {
            printf("44444444447777777777\n");
            continue;
        }
        int l=0,r=k;
        while (r>l)
        {
            int mid=(l+r)/2;
           // cout