Programmers Level5. Number Expression with 1,2,4

Sharing answer codes of mine about Programmers Level5. change124.

Level 5: Number Expression with 1,2,4

Problem Statement

Given a natural number N, find the number expression of N with only 1, 2 and 4. For example,

• Decimal number: 1 → 1
• Decimal number: 2 → 2
• Decimal number: 3 → 4
• Decimal number: 4 → 11
• Decimal number: 5 → 12
• Decimal number: 6 → 14
• Decimal number: 7 → 21

Input:
N = 10

Output:
Answer = 41

Return type is String.

Answer Code (in C++)

#include<iostream>
#include<vector>
#include<string>
using namespace std;

// Think of it as 'chage123' and change 3 to 4 on the 'answer'
string change124(int no)
{
    string answer = "";

  while (no > 0){
    if (no % 3 == 0){
      answer.insert(0, to_string(4)); // Insert the head of string
      no = no/3 - 1; // Special case
    }
    else{
      int rem = no % 3;
      answer.insert(0, to_string(rem)); // Insert the head of string
      no = no/3;
    }
  }

    return answer;
}
int main()
{
    int testNo = 10;
    string testAnswer = change124(testNo);

    cout<<testAnswer;
}

Clever Answer Code (in C++)

#include<iostream>
#include<vector>
using namespace std;

string change124(int no){
    string answer = "";
    int a;
    while(no > 0){
        a = no % 3;
        no = no / 3;
        if (a == 0){
            no -= 1;
        }
        // Interesting way to append
        answer = "412"[a] + answer;
    }

    return answer;
}

int main(){    
    int testNo = 10;
    string testAnswer = change124(testNo);

    cout<<testAnswer;
}