0800. Similar RGB Color

https://leetcode.com/problems/similar-rgb-color

Description

The red-green-blue color "#AABBCC" can be written as "#ABC" in shorthand.

• For example, "#15c" is shorthand for the color "#1155cc".

The similarity between the two colors "#ABCDEF" and "#UVWXYZ" is -(AB - UV)2 - (CD - WX)2 - (EF - YZ)2.

Given a string color that follows the format "#ABCDEF", return a string represents the color that is most similar to the given color and has a shorthand (i.e., it can be represented as some "#XYZ").

Any answer which has the same highest similarity as the best answer will be accepted.

Example 1:

**Input:** color = "#09f166"
**Output:** "#11ee66"
**Explanation:** 
The similarity is -(0x09 - 0x11)2 -(0xf1 - 0xee)2 - (0x66 - 0x66)2 = -64 -9 -0 = -73.
This is the highest among any shorthand color.

Example 2:

**Input:** color = "#4e3fe1"
**Output:** "#5544dd"

Constraints:

• color.length == 7

• color[0] == '#'

• color[i] is either digit or character in the range ['a', 'f'] for i > 0.

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