# 800. Similar RGB Color 相似 RGB 颜色

@TOC

## # 题目描述

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:

1. color is a string of length 7.
2. color is a valid RGB color: for i > 0, color[i] is a hexadecimal digit from 0 to f
3. 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

RGB 颜色用十六进制来表示的话，每个大写字母都代表了某个从 0 到 f 的 16 进制数。 RGB 颜色 "#AABBCC" 可以简写成 "#ABC" 。例如，"#15c" 其实是 "#1155cc" 的简写。 现在，假如我们分别定义两个颜色 "#ABCDEF" 和 "#UVWXYZ"，则他们的相似度可以通过这个表达式 -(AB - UV)^2 - (CD - WX)^2 - (EF - YZ)^2 来计算。 那么给定颜色 "#ABCDEF"，请你返回一个与 #ABCDEF 最相似的 7 个字符代表的颜色，并且它是可以被简写形式表达的。（比如，可以表示成类似 "#XYZ" 的形式）

## # 解题方法

### # 遍历

C++代码如下：

``````class Solution {
public:
string similarRGB(string color) {
vector<string> hexs = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
"a", "b", "c", "d", "e", "f"};
int R = hex2dec(color.substr(1, 2));
int G = hex2dec(color.substr(3, 2));
int B = hex2dec(color.substr(5, 2));
int mostSimilar = INT_MIN;
string res;
for (int i = 0; i < hexs.size(); ++i) {
for (int j = 0; j < hexs.size(); ++j) {
for (int k = 0; k < hexs.size(); ++k) {
string newR = hexs[i] + hexs[i];
string newG = hexs[j] + hexs[j];
string newB = hexs[k] + hexs[k];
int intR = hex2dec(newR);
int intG = hex2dec(newG);
int intB = hex2dec(newB);
int curSimilar = - (R - intR) * (R - intR) - (G - intG) * (G - intG) - (B - intB) * (B - intB);
if (curSimilar > mostSimilar) {
res = "#" + newR + newG + newB;
mostSimilar = curSimilar;
}
}
}
}
return res;
}
int hex2dec(string hex) {
int res = 0;
for (int i = 0; i < hex.size(); ++i) {
if (hex[i] >= 'a') {
res = 16 * res + (hex[i] - 'a' + 10);
} else {
res = 16 * res + (hex[i] - '0');
}
}
return res;
}
};
``````

## # 日期

2019 年 9 月 18 日 —— 今日又是九一八