800. Similar RGB Color

# 800. Similar RGB Color

## 刷题内容

In the following, every capital letter represents some hexadecimal digit from 0 to f.

The red-green-blue color "#AABBCC" can be written as "#ABC" in shorthand.  For example, "#15c" is shorthand for the color "#1155cc".

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

Given the color "#ABCDEF", return a 7 character color that is most similar to #ABCDEF, and has a shorthand (that is, it can be represented as some "#XYZ"

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.
Note:

color is a string of length 7.
color is a valid RGB color: for i > 0, color[i] is a hexadecimal digit from 0 to f
Any answer which has the same (highest) similarity as the best answer will be accepted.
All inputs and outputs should use lowercase letters, and the output is 7 characters.

## 解题方案

- 时间复杂度: O(1)- 空间复杂度: O(1)

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