TTTTTTTTTTTTTT CF 95 B 构造4，7幸运数字贪心构造 string

B. Lucky Numbers

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

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

Input

The only line contains a positive integer n (1 ≤ n ≤ 10^100000). This number doesn't have leading zeroes.

Output

Output the least super lucky number that is more than or equal to n.

Examples

input

output

input

output

题意：给你一个数字（位数<=10^100000）求不小于他且只由4,7并且4跟7的个数相等的最小的数字

#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <cstring>

#include <string>

#include <algorithm>

using namespace std;

#define MM(a,b) memset(a,b,sizeof(a));

char s[100000+10],s2[100000+10];

int main()

{

    string s;

    while(cin>>s)

    {

         int l=s.size();

         if(l%2!=0||s>string(l/2,'7')+string(l/2,'4'))

          {cout<<string(l/2+1,'4')<<string(l/2+1,'7')<<"\n";continue;}

         int n4=l/2,n7=l/2;

         int flag=0;

         string ans;

         for(int i=0;i<s.size();i++)

         {

             int ok=0;

             if(n4>0)

                {

                     if(flag||s[i]<'4') ok=1;

                     else if(s[i]=='4') for(int j=i+1;j<=l;j++)

                     {

                         if(j==l) {ok=1;break;}

                         char ch=j-i<=n7?'7':'4';

                         if(ch>s[j]) ok=1;

                         if(ch!=s[j]) break;

                     }

                }

             if(ok) {ans+="4";n4--;}

             else  {ans+="7";n7--;}

             if(ans[i]>s[i]) flag=1;

         }

         cout<<ans<<"\n";

    }

    return 0;

}

　　分析：比赛时主要是比如4500<7744这样需要构造的数字没想出来。其实还是比较简单的，

因为要让数字足够小，所以从左往右贪心的尽可能的用4，如果当前数字<4，那么肯定就用4了，但是如果等于4呢，那就无法通过当前位判断出来了，需要假设当前位放4，那么为了>=数据4500，接下来的一个位数需要尽可能大，那么就用7，比如47，当到达第三位的时候7>0，说明当前位放4虽然跟数据的数值一样，但是是可以通过后面的数字构造出一个比数据大的，所以当前位放4，否则放7

注意string放元素是a+="w";

巴特西

TTTTTTTTTTTTTT CF 95 B 构造4，7幸运数字贪心构造 string

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巴特西

TTTTTTTTTTTTTT CF 95 B 构造4，7幸运数字 贪心 构造 string

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TTTTTTTTTTTTTT CF 95 B 构造4，7幸运数字贪心构造 string