788. Rotated Digits

#### 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]`.

#### SOLUTION:

``````class Solution {
static int[] rotatedDigitsIndex = new int[10001];
public int rotatedDigits(int N) {
int result = 0;
for(int i = 1;i<=N;i++){
if(rotatedDigitsIndex[i]==1){
result++;
continue;
}else if(rotatedDigitsIndex[i]==0){
String number = i+"";
if((number.contains("2")||number.contains("5")||number.contains("6")||number.contains("9"))
&&(!number.contains("3")&&!number.contains("4")&&!number.contains("7")&&!number.contains("3"))){
result++;
rotatedDigitsIndex[i] = 1;
}else{
rotatedDigitsIndex[i] = -1;
}
}
}
return result;
}
}
``````
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