题目描述：

LeetCode 800. Similar RGB Color

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.

题目大意：

给定RGB格式的颜色代码color，求可以简写为'#XYZ'形式的，与之最接近的颜色代码

color (r, g, b) 与目标 icolor (ir, ig, ib)的距离为 sum((r - ir) ^ 2 + (g - ig) ^ 2 + (b - ib) ^ 2)

解题思路：

蛮力法（Brute Force）

枚举'#XYZ'格式的RGB，记录距离的最小值及其对应的RGB

Python代码：

class Solution(object):
    def similarRGB(self, color):
        """
        :type color: str
        :rtype: str
        """
        ir, ig, ib = (int(color[x: x+2], 16)
                      for x in (1, 3, 5))
        ans = ()
        delta = 0x7FFFFFFF
        for r in range(16):
            for g in range(16):
                for b in range(16):
                    ndelta = sum((ic - c * 17) ** 2
                                 for ic, c in zip((ir, ig, ib), (r, g, b)))
                    if ndelta < delta:
                        delta = ndelta
                        ans = r, g, b
        return '#' + ''.join(hex(c)[2] * 2 for c in ans)

 

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