Rotated Digits

X is a good number if after rotating each digit individually by 180 degrees, we get a valid number that is different from X.  Each digit must be rotated - we cannot choose to leave it alone.
A number is valid if each digit remains a digit after rotation. 0, 1, and 8 rotate to themselves; 2 and 5 rotate to each other (in this case they are rotated in a different direction, in other words, 2 or 5 gets mirrored); 6 and 9 rotate to each other, and the rest of the numbers do not rotate to any other number and become invalid.

Now given a positive number N, how many numbers X from 1 to N are good?

Example:

Input:  n = 10
Output: 4

Approach

Java

public class RotatedDigits {
    public static void main(String[] args) {
        int n = 10;
        System.out.println(rotatedDigits(n));
    }

    static int rotatedDigits(int N) {
        int cnt = 0;
        for (int i = 1; i <= N; i++) {
            int j = i;
            StringBuffer str = new StringBuffer();
            int flag = 0;
            while (j > 0) {
                if (j % 10 == 3 || j % 10 == 4 || j % 10 == 7) {
                    flag = 1;
                    break;
                } else if (j % 10 == 2)
                    str = str.append(5);
                else if (j % 10 == 5)
                    str = str.append(2);
                else if (j % 10 == 6)
                    str = str.append(9);
                else if (j % 10 == 9)
                    str = str.append(6);
                else
                    str = str.append(j % 10);
                j = j / 10;
            }
            str = str.reverse();
            if (flag == 0 && !str.toString().equals(String.valueOf(i)))
                cnt++;
        }
        return cnt;
    }
}

C++

#include <bits/stdc++.h>
using namespace std;

int rotatedDigits(int N)
{
    int cnt = 0;
    for (int i = 1; i <= N; i++)
    {
        int j = i;
        string str = "";
        int flag = 0;
        while (j > 0)
        {
            if (j % 10 == 3 || j % 10 == 4 || j % 10 == 7)
            {
                flag = 1;
                break;
            }
            else if (j % 10 == 2)
                str += "5";
            else if (j % 10 == 5)
                str += "2";
            else if (j % 10 == 6)
                str += "9";
            else if (j % 10 == 9)
                str += "6";
            else
                str += to_string(j % 10);
            j = j / 10;
        }
        reverse(str.begin(), str.end());
        if (flag == 0 && str != to_string(i))
            cnt++;
    }
    return cnt;
}

int main()
{
    int n = 10;
    cout << rotatedDigits(n);
    return 0;
}