 # 带翅膀的猫

## 时光荏苒，我们一直都在 ### 《LeetCode刷题（Easy Rank）：788. Rotated Digits》

3月前  •   •   •   20  •

### 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:

示例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.

### Solution:

JAVAclass Solution {
public int rotatedDigits(int N) {
// Good: 0, 1, 8; 2, 5; 6, 9; Bad: 3, 4, 7
int res = 0;
for (int i = 2; i <= N; i++) {
if (valid(i)) {
res++;
}
}
return res;
}

private boolean valid(int num) {
boolean flag = false;
while (num > 0) {
int digit = num % 10;
if (digit == 3 || digit == 4 || digit == 7) {
return false;
}
if (digit == 2 || digit == 5 || digit == 6 || digit == 9) {
flag = true;
}
num /= 10;
}
return flag;
}
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