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 (on 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:
1 | Input: 10 |
這篇再說給個數值,從1開始列會有幾個數值倒轉還會相同,他也給出2,5:6,9是倒轉相同的例子,那就把數值依序讀入,計算有範例的數值,學到要將數字依序讀入可以轉成字串。
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