Question
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; 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: 10 Output: 4 Explanation: There are four good numbers in the range [1, 10] : 2, 5, 6, 9. Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.
Note:
- N will be in range
[1, 10000]
.
Analyze
Solution
class Solution {
public:
int rotatedDigits(int N) {
int res = 0;
for (int i = 0; i <= N; ++i) {
if( isRotatedDigits(i) ) ++res;
}
return res;
}
bool isRotatedDigits(int number) {
int digit = 0;
bool good_flag = false;
while(number) {
digit = number % 10;
if(number) number = number / 10;
if (digit == 3 || digit == 4 || digit == 7) return false;
else if (digit == 0 || digit == 1 || digit == 8 ) continue;
else {
good_flag = true;
}
}
return good_flag;
}
};