Similar RGB Color — LeetCode 800 Python Solution

The problem

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

Example

Input

color = "#09f166"

Output

"#11ee66"

Explanation

The similarity is -(0x09 - 0x11)2 -(0xf1 - 0xee)2 - (0x66 - 0x66)2 = -64 -9 -0 = -73.

Python solution

class Solution:
    def similarRGB(self, color: str) -> str:
        def f(x):
            y, z = divmod(int(x, 16), 17)
            if z > 8:
                y += 1
            return '{:02x}'.format(17 * y)

        a, b, c = color[1:3], color[3:5], color[5:7]
        return f'#{f(a)}{f(b)}{f(c)}'

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 800. Similar RGB Color is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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