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g0701_0800.s0788_rotated_digits.readme.md Maven / Gradle / Ivy

788\. Rotated Digits

Medium

An integer `x` is a **good** 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. For example:

*   `0`, `1`, and `8` rotate to themselves,
*   `2` and `5` rotate to each other (in 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.

Given an integer `n`, return _the number of **good** integers in the range_ `[1, n]`.

**Example 1:**

**Input:** n = 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.

**Example 2:**

**Input:** n = 1

**Output:** 0

**Example 3:**

**Input:** n = 2

**Output:** 1

**Constraints:**

*   1 <= n <= 104