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]
.
解题思路:输入N,判断数字是否是good数字。旋转180度变成另一个数,2 5 6 9旋转后是good数字。0 1 8旋转后是本身
含有3 4 7的不是good数字
class Solution { public: int rotatedDigits(int N) { int count=0; for(int i=1;i<=N;i++){ if(judge(i)){ count++; } } return count; } bool judge(int N){ bool flag=false; while(!(N%10==0&&N/10==0)){ int k=N%10; if(k==3||k==4||k==7){ flag=false; break; } if(k==2||k==5||k==6||k==9){ flag=true; } N/=10; } return flag; } };