如何使用正则表达式验证十六进制颜色代码

给定字符串str ，任务是使用正则表达式检查字符串是否为有效的十六进制颜色代码。

The valid hexadecimal color code must satisfy the following conditions. 
 

1. It should start from ‘#’ symbol.
2. It should be followed by the letters from a-f, A-F and/or digits from 0-9.
3. The length of the hexadecimal color code should be either 6 or 3, excluding ‘#’ symbol.

例如：#abc、#ABC、#000、#FFF、#000000、#FF0000、#00FF00、#0000FF、#FFFFFF 都是有效的十六进制颜色代码。
例子：

Input: str = “#1AFFa1”; 
Output: true 
Explanation: 
The given string satisfies all the above mentioned conditions.
Input: str = “#F00”; 
Output: true 
Explanation: 
The given string satisfies all the above mentioned conditions.
Input: str = “123456”; 
Output: false 
Explanation: 
The given string doesn’t start with a ‘#’ symbol, therefore it is not a valid hexadecimal color code.
Input: str = “#123abce”; 
Output: false 
Explanation: 
The given string has length 7, the valid hexadecimal color code length should be either 6 or 3. Therefore it is not a valid hexadecimal color code.
Input: str = “#afafah”; 
Output: false 
Explanation: 
The given string contains ‘h’, the valid hexadecimal color code should be followed by the letter from a-f, A-F. Therefore it is not a valid hexadecimal color code. 

方法：这个问题可以通过使用正则表达式来解决。

• 获取字符串。
• 创建一个正则表达式来检查有效的十六进制颜色代码，如下所述：

regex = "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$";

• 在哪里：
  • ^代表字符串的开始。
  • #表示十六进制颜色代码必须以“#”符号开头。
  • (代表组的开始。
  • [A-Fa-f0-9]{6}表示来自 af、AF 的字母或 0-9 的数字，长度为 6。
  • |代表或。
  • [A-Fa-f0-9]{3}表示来自 af、AF 的字母，或长度为 3 的 0-9 数字。
  • )代表组的结束。
  • $表示字符串的结尾。
• 将给定的字符串与正则表达式匹配，在Java，这可以通过使用 Pattern.matcher() 来完成。
• 如果字符串与给定的正则表达式匹配，则返回 true，否则返回 false。

下面是上述方法的实现：

C++

// C++ program to validate the
// hexadecimal color code using Regular Expression
#include 
#include 
using namespace std;
 
// Function to validate the hexadecimal color code.
bool isValidHexaCode(string str)
{
 
  // Regex to check valid hexadecimal color code.
  const regex pattern("^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$");
 
  // If the hexadecimal color code
  // is empty return false
  if (str.empty())
  {
     return false;
  }
 
  // Return true if the hexadecimal color code
  // matched the ReGex
  if(regex_match(str, pattern))
  {
    return true;
  }
  else
  {
    return false;
  }
}
 
// Driver Code
int main()
{
   
  // Test Case 1:
  string str1 = "#1AFFa1";
  cout << str1 + ": " << isValidHexaCode(str1) << endl;
 
  // Test Case 2:
  string str2 = "#F00";
  cout << str2 + ": " <<  isValidHexaCode(str2) << endl;
 
  // Test Case 3:
  string str3 = "123456";
  cout << str3 + ": " <<  isValidHexaCode(str3) << endl;
 
  // Test Case 4:
  string str4 = "#123abce";
  cout << str4 + ": " <<  isValidHexaCode(str4) << endl;
 
  // Test Case 5:
  string str5 = "#afafah";
  cout << str5 + ": " <<  isValidHexaCode(str5) << endl;
 
  return 0;
}
 
// This code is contributed by yuvraj_chandra

Java

// Java program to validate hexadecimal
// colour code using Regular Expression
 
import java.util.regex.*;
 
class GFG {
 
    // Function to validate hexadecimal color code .
    public static boolean isValidHexaCode(String str)
    {
        // Regex to check valid hexadecimal color code.
        String regex = "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$";
 
        // Compile the ReGex
        Pattern p = Pattern.compile(regex);
 
        // If the string is empty
        // return false
        if (str == null) {
            return false;
        }
 
        // Pattern class contains matcher() method
        // to find matching between given string
        // and regular expression.
        Matcher m = p.matcher(str);
 
        // Return if the string
        // matched the ReGex
        return m.matches();
    }
 
    // Driver Code.
    public static void main(String args[])
    {
 
        // Test Case 1:
        String str1 = "#1AFFa1";
        System.out.println(
            str1 + ": "
            + isValidHexaCode(str1));
 
        // Test Case 2:
        String str2 = "#F00";
        System.out.println(
            str2 + ": "
            + isValidHexaCode(str2));
 
        // Test Case 3:
        String str3 = "123456";
        System.out.println(
            str3 + ": "
            + isValidHexaCode(str3));
 
        // Test Case 4:
        String str4 = "#123abce";
        System.out.println(
            str4 + ": "
            + isValidHexaCode(str4));
 
        // Test Case 5:
        String str5 = "#afafah";
        System.out.println(
            str5 + ": "
            + isValidHexaCode(str5));
    }
}

Python3

# Python3 program to validate
# hexadecimal colour code using
# Regular Expression
import re
 
# Function to validate
# hexadecimal color code .
def isValidHexaCode(str):
 
    # Regex to check valid
    # hexadecimal color code.
    regex = "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$"
 
    # Compile the ReGex
    p = re.compile(regex)
 
    # If the string is empty
    # return false
    if(str == None):
        return False
 
    # Return if the string
    # matched the ReGex
    if(re.search(p, str)):
        return True
    else:
        return False
 
# Driver Code.
 
# Test Case 1:
str1 = "#1AFFa1"
print(str1, ":", isValidHexaCode(str1))
 
# Test Case 2:
str2 = "#F00"
print(str2, ":", isValidHexaCode(str2))
 
# Test Case 3:
str3 = "123456"
print(str3, ":", isValidHexaCode(str3))
 
# Test Case 4:
str4 = "#123abce"
print(str4, ":", isValidHexaCode(str4))
 
# Test Case 5:
str5 = "#afafah"
print(str5, ":", isValidHexaCode(str5))
 
# This code is contributed by avanitrachhadiya2155

输出：

#1AFFa1: true
#F00: true
123456: false
#123abce: false
#afafah: false

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