AtCoder Beginner Contest 336 C - Even Digits题解

C - Even Digits Editorial

Time Limit: 2 sec / Memory Limit: 1024 MB

Score: 300300 points

Problem Statement

A non-negative integer �n is called a good integer when it satisfies the following condition:

• All digits in the decimal notation of �n are even numbers (00, 22, 44, 66, and 88).

For example, 00, 6868, and 20242024 are good integers.

You are given an integer �N. Find the �N-th smallest good integer.

Constraints

• 1≤N≤10^12
• N is an integer.

Input

The input is given from Standard Input in the following format:

N

Output

Print the N-th smallest good integer.

Sample Input 1Copy

Copy

8

Sample Output 1Copy

Copy

24

The good integers in ascending order are 0,2,4,6,8,20,22,24,26,28,…0,2,4,6,8,20,22,24,26,28,….
The eighth smallest is 2424, which should be printed.

Sample Input 2Copy

Copy

133

Sample Output 2Copy

Copy

2024

Sample Input 3Copy

Copy

31415926535

Sample Output 3Copy

Copy

200662886824422

题解：

要精用vector，防止超时。

#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<int> a;//类似高精度
int n;
signed main()
{
ios::sync_with_stdio(false);
cin.tie();
cout.tie();
cin >> n;
n-=1;//因为第一位是0嘛
while(n > 0){//25=10进位了
a.push_back(n%5);
n /= 5;
}
if(a.empty()) a.push_back(0);
for(int i = a.size()-1; i > -1; i--)//迭代器，也不算吧，vector也是数组
cout << 2a[i];
}