如何统计字符串中连续出现超2次的下划线占位符出现次数

Got it, let's revamp your original code to meet the new requirement: counting only placeholder sequences where 3 or more consecutive underscores appear (single or double underscores don't count as valid placeholders).

Approach 1: Iterative Counting (Explicit Loop) #

This method gives you full control over the counting logic, which is great for clarity if you need to adjust rules later. Here's the modified code with comments:

void Main() 
{
    string someString = "Fill ________ and ______ this";
    char targetChar = '_';
    int validPlaceholderCount = 0;
    int currentConsecutiveCount = 0;

    // Iterate through each character in the string
    foreach (char c in someString)
    {
        if (c == targetChar)
        {
            // Increment counter when we hit an underscore
            currentConsecutiveCount++;
        }
        else
        {
            // Check if we just finished a valid placeholder (3+ underscores)
            if (currentConsecutiveCount > 2)
            {
                validPlaceholderCount++;
            }
            // Reset the counter for the next potential sequence
            currentConsecutiveCount = 0;
        }
    }

    // Don't forget to check the last sequence if the string ends with underscores!
    if (currentConsecutiveCount > 2)
    {
        validPlaceholderCount++;
    }

    Console.WriteLine($"Valid placeholders found: {validPlaceholderCount}");
    // Output for your example string: 2
}

Key notes for this approach:

• We track currentConsecutiveCount to keep tabs on how many underscores we've seen in a row.
• When we hit a non-underscore character, we check if the previous sequence was long enough to be a valid placeholder.
• We add a final check after the loop to catch cases where the string ends with a valid placeholder sequence.

Approach 2: Regular Expressions (Shorter Code) #

If you prefer a more concise solution, regular expressions are perfect here. We can match all sequences of 3 or more underscores in one go:

using System.Text.RegularExpressions;

void Main()
{
    string someString = "Fill ________ and ______ this";
    // Regex pattern: match 3 or more consecutive underscores
    MatchCollection placeholderMatches = Regex.Matches(someString, @"_{3,}");
    
    // The number of matches is our valid placeholder count
    int validPlaceholderCount = placeholderMatches.Count;

    Console.WriteLine($"Valid placeholders found: {validPlaceholderCount}");
    // Also outputs 2 for your example
}

This method is great for simple pattern matching—less code to write and read. The @{3,} pattern means "match the underscore character 3 or more times consecutively".

Test Cases to Verify #

• Input: "Single _ here" → Output: 0 (only one underscore)
• Input: "Two __ separate __ underscores" → Output: 0 (two sequences of two underscores each)
• Input: "Your example: Fill ________ and ______ this" → Output: 2 (two sequences of 8 and 6 underscores)

内容的提问来源于stack exchange，提问作者Nody